&EPA
United States
Environmental Protection
Agency
January 2013
Rainwater Harvesting
Conservation, Credit, Codes, and Cost
Literature Review and Case Studies
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Disclaimer
This document provides information for states, territories, and federally recognized tribes for
developing and implementing rainwater harvesting programs. At times, this document refers to
statutory and regulatory provisions, which contain legally binding requirements. This document
does not substitute for those provisions or regulations, nor is it a regulation itself. Thus it does
not impose legally-binding requirements on EPA, states, territories, authorized tribes, or the
public and may not apply to a particular situation based upon the circumstances.
EPA, state, territory, and authorized tribe decision makers retain the discretion to adopt
approaches toward rainwater harvesting that differ from this document. EPA may change this
document in the future.
Reference herein to any specific commercial products, process, or service by trade name,
trademark, manufacturer, or otherwise, does not necessarily constitute or imply its
endorsement, recommendation, or favoring by the United States Government. The views and
opinions of authors expressed herein do not necessarily state or reflect those of the United
States Government, and shall not be used for advertising or product endorsement purposes.
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Rainwater Harvesting:
Conservation, Credit, Codes, and Cost
Literature Review and Case Studies
Contact Information
For more information, questions, or comments about this document, contact
Chris Solloway at U.S. Environmental Protection Agency, Office of Water,
Office of Wetlands, Oceans, and Watersheds, 1200 Pennsylvania Avenue, Mail
Code 4503T, Washington, DC 20460, or by email at
Solloway.Chris@epamail.epa.gov.
January 2013
EPA-841-R-13-002
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Acknowledgements
This document was prepared by the U.S. Environmental Protection Agency (EPA), Office of
Water, Office of Wetlands, Oceans, and Watersheds. The EPA Project Manager for this
document was Chris Solloway, who provided overall direction and coordination. EPA was
supported in the development of this document by The Low Impact Development Center, Inc
and Geosyntec Consultants.
m
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TABLE OF CONTENTS
1. INTRODUCTION 1
2. LITERATURE REVIEW SUMMARY 2
2.1 Water Conservation 2
2.1.1 Technical 2
2.1.2 Operation and Maintenance 5
2.1.3 Programmatic 6
2.1.4 Predictability 6
2.2 Stormwater Runoff Volume and Pollutant Load Reduction 9
2.2.1 Technical 10
2.2.2 Operation and Maintenance 12
2.2.3 Programmatic 12
2.2.4 Predictability 14
2.3 Code and Administration 15
2.3.1 Technical 15
2.3.2 Operation and Maintenance 19
2.4 Cost Factors 22
2.4.1 Technical 23
2.4.2 Operation and Maintenance 23
2.4.3 Programmatic 24
2.4.4 Predictability 25
3. CONSIDERATIONS REQUIRING ADDITIONAL RESEARCH 28
4. SUMMARY AND RECOMMENDATIONS 30
4.1 Findings 30
4.2 Recommendations 31
5. CASE STUDIES 32
6. REFERENCES 33
IV
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1. INTRODUCTION
Rainwater harvesting has been used throughout history as a water conservation measure,
particularly in regions where other water resources are scarce or difficult to access. In recent
years, researchers and policy makers have shown renewed interest in water use strategies due to
rising water demand, increased interest in conservation (both water and energy), and an
increased regulatory emphasis on reducing stormwater runoff volumes and associated pollutant
loads. In the last decade, as interest in the practice has grown, numerous state, municipal, and
regional agencies have adopted or amended codes and guidelines to encourage responsible and
effective rainwater harvesting practices. In addition, researchers from universities and non-
government organizations, as well as industry consultants, have published papers and articles
addressing a broad range of topics related to the installation, maintenance, costs, and
performance of harvest and use systems.
A literature review of existing research and policy documents related to rainwater harvesting has
been conducted, with particular focus on characterizing the current state of the practice in the
areas of: (1) water conservation, (2) stormwater volume and pollutant load reduction, (3) code
and administration considerations and (4) cost factors. The purpose of this report is to summarize
the existing knowledge base in these four areas, assess factors affecting economic benefits of
rainwater harvesting, and identify topics requiring additional research. This report is not intended
to serve as a design document. Readers looking for design guidance should consult a more
technically-focused publication, such as the Texas Manual on Rainwater Harvesting (TWDB,
2005).
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2. LITERATURE REVIEW SUMMARY
The literature review conducted focused on the impacts of rainwater harvesting in the areas of
water conservation, stormwater runoff volume, and pollutant load reduction; code and
administration; and cost factors. The review included relevant information for a range of system
sizes and complexities from small, passive systems (e.g. rain barrels) to larger systems with
fitted pumps, controls, and treatment systems (e.g. active systems or cisterns). For each
assessment topic, the primary considerations for literature review were as follows:
Technical - The scientific, engineering, and design elements associated with each topic and how
the technical components of a rainwater harvesting system affect performance, compliance, and
cost.
Operation and Maintenance - The practical, day-to-day, and periodic activities and costs
associated with effectively operating a rainwater harvesting system.
Programmatic - The current regulatory environment related to rainwater harvesting,
including examples of code modifications, incentive programs, and public outreach.
Predictability - Reliability of present and future performance of rainwater harvesting
systems relative to each assessment topic.
The results of the literature review for each assessment topic are summarized in the following
sections.
2.1 Water Conservation
Throughout history, rainwater harvesting has been viewed primarily as a fresh water supply or
water conservation practice. In the western United States, conservation continues to serve as a
primary driver for rainwater harvesting as the region struggles to meet the water demands of its
burgeoning population. This section provides a basic technical description of the two main types
of rainwater harvesting systems (passive and active) and outlines the basic maintenance
requirements of each. Examples of code requirements and the need for predictability of water
demand are also discussed.
2.1.1 Technical
Passive harvesting systems (e.g. rain barrels) are typically small volume (50-100 gallon) systems
designed to capture rooftop runoff. Rain barrels are commonly used in residential applications
where flow from rain gutter downspouts is easily captured for outdoor uses such as garden and
landscape irrigation or car washing. Due to their smaller sizes and ease of siting, passive systems
are generally installed at grade, making impact from sunlight on the stored water a consideration.
Direct and indirect sunlight will act as a catalyst for algae growth in the cistern, so exposure to
sunlight should be limited where possible. Most above-ground cisterns are available in opaque
colors or made from opaque materials, and are recommended. Cisterns made of translucent
materials such as light colored plastics should be avoided.
Water is extracted from the rain barrels through a spigot typically with no connections to internal
or external plumbing. Due to the small volumes and lack of additional treatment, the water
collected in rain barrels is not used indoors (even for non-potable uses), and most state and local
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regulations require clear markings indicating that the water is non-potable. In addition, rain
barrels are generally required to be screened to prevent vectors from breeding and secured to
avoid creating a drowning hazard. Passive systems are typically designed with an overflow to
ground surface or the existing stormwater collection system. The Memorandum of
Understanding on permitting requirements for Rainwater Harvesting Systems located within the
City and County of San Francisco provides an excellent overview of the design and maintenance
requirements for rain barrels and allowable uses for harvested water.
Active harvesting systems (e.g. cisterns) are larger volume (typically 1,000 - 100,000 gallon)
systems which capture runoff from roofs or other suitable surfaces (e.g., terraces, walkways,
grassed areas and with proper pre-treatment, parking lots), provide water quality treatment, and
use pumps or sufficient head1 to supply water to a distribution system. Cisterns may be made of
wood, plastic, metal, or concrete depending on the size and desired location (Hunt and Szpir,
2006). As noted above, cisterns installed at ground surface should be fabricated from opaque
materials to limit penetration of light and resulting promotion of algae growth.
Implementation of these systems usually requires significant design effort to: 1) determine
optimal cistern sizing based on collection and water demand characteristics, 2) identify suitable
cistern locations, 3) engineer piping and related drainage configurations, 4) incorporate water
quality treatment, and 5) configure an appropriate distribution system for the harvested water.
Rainwater collected in active systems is typically used for irrigation or for indoor non-potable
water replacement (e.g. toilet flushing, clothes washing, evaporative cooling, etc.). The type and
complexity of treatment systems depend on the intended use of the harvested water as well as the
water quality and permitting requirements in a particular location. Several states - including
Georgia, North Carolina, Texas, and Virginia - have produced guidance manuals which provide
information about the types of treatment systems and components available for meeting specific
water quality objectives. At the municipal level, several major cities - including Los Angeles,
San Francisco, Tucson, and Portland - have released guidance and/or policy documents
addressing treatment and permitting requirements for rainwater harvesting systems. Treatment
devices can range from simple to complex; some examples include first flush diverters, screen
filters, ultraviolet light disinfection, ozone treatment, chlorination, and reverse osmosis (TWDB,
2005).
Active rainwater harvesting systems are typically fitted with one or more pumps, electronic
water level sensors, system controllers, and water treatment systems and are often supported by
municipal or private well water supplies as a back-up water source. These integrated systems are
intended to functionally mimic the delivery of domestic water, and are usually connected to
back-up supplies through the use of plumbing cross-connections with backflow prevention or air
gap based water feeds. The intent of the integrated back-up water supply is to provide
uninterrupted water delivery for instances where harvested water is depleted.
This integration prioritizes the use of rainwater before the municipal supply and maximizes its
use. When the supply of harvested water runs out, the integrated system automatically switches
1 Large cistern systems located on rooftops or otherwise elevated to provide sufficient driving head to facilitate
connections to a distribution system without the need for pumping are also classified as 'Active' systems in this
context.
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to the municipal supply with little or no disruption in flow. In many areas, state or local
regulations restrict the use of cross-connections with mechanical backflow prevention and
require that the municipal supply be used to fill small day tanks or to partially refill cisterns
directly. In cross-connection configurations, the municipal water feed is directly plumbed to the
same water distribution system fed by the harvesting system. It is isolated by automated control
valves and passive check valves to prevent the harvested water from flowing into the domestic
water supply lines. More positive isolation of these water sources is provided via a backflow
prevention device with an internal 'reduced pressure' zone which maintains a lower pressure
chamber in the device that obviates flow or suction in the direction opposite normal flow. As
such, this device is commonly referred to as a 'reduced pressure zone backflow preventer', an
'RPZ device', or an 'RPZ valve'. Most jurisdictions where RPZ backflow preventers are allowed
require the devices be tested periodically. Cross connection regulation is further addressed in this
document in the Code and Administration section.
Where cross connection configurations are prohibited, integration of a back-up water supply is
provided by partially refilling the cistern or a smaller ancillary day tank, with an air gap at the
end of the refill pipe to prevent cross-contamination between the cisterns and the back-up water
supply. In such systems, the back-up water supply is triggered (through a level sensor or float-
controlled valve) slightly before the cistern or ancillary tank runs out of water, partially refilling
the tank to some pre-determined level to ensure supply for applied water demands. Refill designs
that provide for refilling of a main cistern versus a day tank will have reduced overall system
performance compared to integrated designs with cross-connections because a portion of the
storage volume is consumed by municipal water refill, impacting the volume available for
harvesting and stormwater control.
The water conservation performance of active systems is significantly better than that of passive
systems (e.g. rain barrels) due to two primary factors: storage volumes and delivery systems.
As noted above, passive systems are typically implemented with small volume storage
commensurate with catchment areas associated with single roof downspout collection areas. For
small systems, the ability to store water between rain events is the most significant factor in a
harvesting system's performance. Because of the logistics of collection from distributed roof
collection points, small volumes and limited use are almost universally associated with passive
systems.
Further limiting the performance of passive systems is the nature of the water delivery system.
Since passive systems are by definition not fitted with pumps for pressurizing the water extracted
for delivery, their use is usually limited to refilling watering buckets or connection to ground
irrigation systems fed over limited distances by gravity. For systems with favorable geometry in
terms of elevation and distance to end use locations, these systems can be quite useful. These
types of systems are commonly used in the developing world; however, widespread
implementation in the United States has been limited.
The demand for potable and non-potable water - and therefore the potential for water
conservation - varies significantly with factors such as climate, land use, and development type.
Determining appropriate system sizing requires an accurate quantitative analysis of water
demand relative to regional precipitation patterns. This is addressed in more detail under the
discussion on Predictability.
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2.1.2 Operation and Maintenance
In general, passive systems require only minor maintenance at little or no cost to the system
owner. The City and County of San Francisco, CA list some basic guidelines for rain barrel
maintenance in a 2008 Memorandum of Understanding between the San Francisco Public
Utilities Commission, Department of Building Inspection, and Department of Public Health.
These guidelines include: keeping rain barrels clear of debris and maintaining all screens and
inlet filtration to prevent clogging and vector breeding; annual cleaning of rain barrels with a
non-toxic cleaner; clearing debris from the catchment area periodically and using the collected
rainwater as soon as possible after each rain event to prevent bacteria growth and provide
capacity for capturing the next rain event (City and County of San Francisco, 2008).
Active systems have similar basic maintenance requirements to passive systems, namely debris
removal and filter maintenance (City and County of San Francisco, 2008). Because active
systems are larger and typically include more components, some additional maintenance may be
required depending on the design. For example, most active systems include some type of
filtration device or capability upstream of the point of connection of the collection system to the
cisterns. Pre-cistern filtration systems, such as filter baskets or vortex filters to capture
particulates and gross solids, require periodic maintenance to prevent clogging unless
implemented with self-cleaning capability or mechanisms. Cisterns also generally have longer
residence times than rain barrels due to their larger storage volumes. As a result, biofilms or
aeration devices may be incorporated to prevent algal or bacterial growth (Cabell Brand Center,
2009). Periodic tank inspection is recommended; periodic cleaning and/or disinfection should be
performed on an as-needed basis, and should be incorporated into a system maintenance plan in
applications where catchment surfaces are exposed to significant debris loading from leaves,
trash, pollen, and other elements. Pumps in active systems also require periodic maintenance and
replacement. While the exact maintenance requirements depend on the type and configuration of
the pump and its usage pattern, general requirements include testing of triggers and float
switches and flushing to prevent clogging. The Virginia Rainwater Harvesting Manual provides
information on different types of pump configurations and preventive maintenance
considerations (Cabell Brand Center, 2009). Finally, fine filtration and water quality adjustment
downstream of the pumping system but before distribution piping is common to all but the
simplest of outdoor applications, and requires either self-cleaning devices or a periodic
maintenance schedule to ensure proper operation of those components.
Inspection and maintenance schedules vary depending on the type of system and the intended use
of harvested water. The table below provides guidance on basic maintenance requirements for
cistern systems.
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Table 1: Suggested Maintenance Procedures for Rainwater Harvesting Systems
Activity
Keep gutters and downspouts free of leaves and other debris
Inspect and clean pre-screening, inlet filtration devices, and first flush
diverters
Inspect and clean storage tank lids, paying special attention to vents and
screens on inflow and outflow spigots. Check mosquito screens
and patch holes or gaps immediately
Inspect condition of overflow pipes, overflow filter path, and/or secondary
runoff reduction practices
Inspect tank for sediment buildup
Clear overhanging vegetation and trees over roof surface
Check integrity of backflow preventer (unless required more frequently by
state or local regulations)
Inspect structural integrity of tank, pump, pipe, and electrical system
Replace damaged or defective system components
Frequency
O: Twice a year
O: Four times a year
O: Once a year
O: Once a year
I: Every third year
I: Every third year
I: Every third year
I: Every third year
I: Every third year
Key: O = Owner; I = qualified third party Inspector
Source: Virginia DCR Stormwater Design Specification No. 6 - Rainwater Harvesting
2.1.3 Programmatic
There are currently no federal regulations governing rainwater harvesting for non-potable use,
and the policies and regulations enacted at the state and local levels vary widely from one
location to another. Regulations are particularly fragmented with regard to water conservation, as
the permissible uses for harvested water tend to vary depending on the climate and reliability of
the water supply. The level of detail in these regulations also varies from one location to another.
In the past, many plumbing codes have not formally defined rainwater harvesting as a practice
distinct from water recycling, resulting in more stringent requirements than seemingly necessary.
In contrast, cities and counties looking to promote water conservation have begun issuing
policies that better define harvested water and its acceptable uses. The City of Portland (Oregon),
for example, provides explicit guidance on the accepted uses of harvested water both indoors and
outdoors. In January 2010, Los Angeles County issued a policy providing a clear, regulatory
definition of "rainfall/non-potable cistern water" and drawing a specific distinction between
harvested water and grey or recycled water (County of Los Angeles, 2010). These and other
issues are discussed in greater detail in the Code and Administration section.
2.1.4 Predictability
As mentioned previously, the efficacy of a rainwater harvesting system for conserving water
depends largely on the ability to balance water demands with the water supply provided by
regional precipitation. The ability of a rainwater harvesting system to meet water demands using
the supply of available rainwater is typically expressed in terms of Satisfaction (or Utilization)
and Reliability (Thomas, 2004; Liaw and Tsai, 2004). Satisfaction refers to the percent of water
demands met or projected to be met by the harvesting system over the entire time period
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analyzed. Reliability refers to the percentage of individual time units (e.g. days) in the time
period analyzed that the imposed water demands are entirely met by the system.
Regional climate conditions often play a significant role in determining the reliability of a
particular system design. For example, in climates where the majority of rainfall occurs in a
single season, systems may be storage-constrained as practical limitations in cistern size prevent
storage of sufficient rainfall volume to meet water demand during the dry season. Ideally, on-site
use demands would meet or exceed the maximum supply volume over a relatively short duration
(TWDB, 2006). In reality, however, matching supply and demand may be quite difficult. The
highest performance for a given area will be achieved where water demands imposed on the
harvesting system are present contemporaneously with precipitation patterns. Many parts of the
eastern U.S., for example, have relatively consistent precipitation patterns across the 12 months
of the year. Applying 12-month demands such as toilet water or industrial demands to this
rainfall pattern has the potential to realize very strong system performance given proper sizing.
The use of rainwater harvesting systems as a stormwater control measure adds additional
complexity as it requires a balance between providing sufficient stored water to meet demands
while maintaining adequate cistern capacity to capture anticipated stormwater runoff.
The ability to accurately predict both supply and demand has a significant impact on both the
water conservation and stormwater volume reduction performance of harvesting systems. As a
result, water usage estimates are often used along with detailed rainfall and climate data to
develop a water budget analysis for a particular site. This analysis predicts the water
conservation and stormwater runoff reduction performance of a rainwater harvesting system as a
function of tank size, and allows for the selection of the optimum cistern size to meet design
goals. In comparing discrete rainfall patterns from a particular region with anticipated on-site
water demands, water budget analyses also provide a good indication of the efficacy of rainwater
harvesting for a particular climate region. Additional information on water budget analysis is
provided in the section on Stormwater Runoff Volume and Pollutant Load Reduction.
In developing a water budget analysis, it is necessary to understand the proposed uses for
harvested water and the demand rates and patterns associated with those uses. While site-specific
data are preferable for system design, a number of studies are available which can provide
planning level estimates of water use for different parts of the United States.
The American Water Works Association (AWWA) estimates the average total per capita water
use at 172 gallons per capita per day (gpcd), with 101 gpcd coming from outdoor uses, 69.3 gpcd
coming from indoor uses and 1.7 gpcd from unknown or unidentified indoor or outdoor use.
Residential indoor uses and their respective percentages of total indoor use (69.3 gpcd) are
estimated to be: showers (16.8%), clothes washers (21.7%), dishwashers (1.4%), toilets (26.7%),
baths (1.7%), leaks (13.7%), faucets (15.7%), and other domestic uses (2.2%) (AWWA, 1999).
Of these, toilets and clothes washers have been suggested as ideal potable demand replacements
using either reclaimed greywater or harvested rainwater, which could supply up to a total of
approximately 48.3% of the total typical demand (Hunt and Szpir, 2006; Gold et al, 2010).
The Pacific Institute has published similar data based on a study of water use in California; in
addition to residential use, this study also considers water use at commercial, industrial, and
institutional facilities (Pacific Institute, 2003). Section 4 of the Pacific Institute Report provides a
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detailed discussion of end uses of water in the commercial, industrial, and institutional (CII)
sector. The study considers a broad range of development types, including hospitals, hotels,
office buildings, and manufacturing facilities. For the CII sector as a whole, end uses and their
respective percentages of total use are provided as follows: landscaping (35%), kitchen (6%),
cooling (15%), restroom (16%), process (17%), laundry (2%), and other (9%). Toilet flushing is
estimated to account for 72% of restroom water use in the CII sector (Pacific Institute, 2003). It
should be noted that these values represent averages over a variety of development types. The
figure below summarizes the proportion of total water use attributed to different end uses as a
function of development type.
End Uses as a Percent of Total Water Use
70%
60%
Total Non-Potable End Uses:
Residential -78%
Commercial/Industrial -64%
I Residential
I Commerce I/Industrial
10%
0%
Landscaping/
Outdoor Use
Toilets
Other Restroom
Use
Laundry
Other
Kitchen
Cooling
Process Water
End Use
1 - Residential end uses based on AWWA (1999).
2 Commercial/Industrial end uses based on Pacific Institute (2003).
The AWWA has also published water usage estimates for a variety of commercial and industrial
development types (AWWA, 2000). These data show separate estimates for different end use
types based on studies conducted in several cities across the U.S. The differences in these
estimates may be significant based on climate and other regional factors. Schools in Phoenix, for
example, spend a significantly higher proportion of total water use on landscape irrigation (54%)
as compared to Denver (29%). Morales et al. present an alternative method for estimating water
use at commercial, industrial, and institutional facilities based on heated building area and other
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parcel-level attributes (Morales, 2009). Additional resources for water usage estimates are
provided in the Recommended Resources at the end of this section.
The significant proportion of water use attributed to non-potable uses demonstrate the potential
for water conservation benefits through rainwater harvesting. It should be noted, however, that
the data presented here are average values, which may be subject to significant variability, and
should not be used in lieu of site-specific data for individual harvesting system designs.
Water Conservation Links to Recommended Resources
Codes and Policy Documents:
City and County of San Francisco:
Rainwater Harvesting in San Francisco
Guidance Documents:
Texas Water Development Board:
The Texas Manual on Rainwater Harvesting, 3rd Edition
Georgia Department of Community Affairs:
Georgia Rainwater Harvesting Guidelines
Research Documents:
Water Use Statistics:
American Water Works Association (AWWA):
Commercial and Institutional End Uses of Water
Residential End Uses of Water
Pacific Institute:
Waste Not, Want Not: The Potential for Urban Water Conservation in
California
2.2 Stormwater Runoff Volume and Pollutant Load Reduction
In addition to providing a water conservation benefit, rainwater harvesting systems are also
recognized as a Low Impact Development (LID) technique for stormwater management. By
retaining stormwater runoff for on-site use, harvesting systems reduce the runoff volumes and
pollutant loads entering the stormwater collection system, helping to restore pre-development
hydrology and mitigate downstream water quality impacts. As a result, many state and local
governments have begun to encourage the use of rainwater harvesting as a stormwater Best
Management Practice (BMP). This section discusses the technical design and operational
considerations associated with the use of rainwater harvesting for stormwater management,
provides an overview of some regulatory and incentive programs for stormwater runoff
reduction, and outlines methods for maintaining available storage volume to ensure reliable
performance.
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2.2.1 Technical
While passive rainwater harvesting systems can be fairly easy to implement (as discussed
previously), they present limited opportunity for significant reduction in stormwater runoff due
to their relatively small volume, and an inability to ensure that stormwater retention volume is
available at the onset of precipitation events. These limitations lead to the need for strong
outreach campaigns and dissemination of operational guidance with deployment of these
systems, as well as widespread implementation in order to achieve the significant stormwater
flow reduction benefits. City-wide green initiatives, such as those undertaken in New York and
Los Angeles, have attempted to address the need for widespread implementation by sponsoring
rain barrel giveaways and engaging the public using new and social media. Public education
about the stormwater benefits of rainwater harvesting and the importance of managing storage
volume through responsible and reliable water demand is a significant step toward improving the
stormwater performance of passive systems.
Unlike rain barrels, well-designed active harvesting systems can provide greater flexibility for
managing stormwater runoff because they are sized based on an analysis of local precipitation
and site-specific demand. Tank sizing for stormwater performance requires a detailed water
budget analysis which considers the size of the catchment area, local precipitation patterns and
anticipated indoor and outdoor water use. While some guidance manuals recommend use of
monthly average precipitation data in cistern sizing, these data fail to capture the discrete size
and distributional characteristics of shorter daily or intra-daily rainfall events which have
significant implications for stormwater performance.
A better approach is to use a long-term, continuous record of hourly or daily precipitation data
(available from the National Climatic Data Center) for a given location (Cabell Brand Center,
2009). The continuous record of precipitation can be analyzed in a spreadsheet model along with
anticipated demands to provide more precise estimates of water conservation and stormwater
performance as a function of cistern volume for a given catchment area and demand scenario.
The designer can use the results to identify the most cost effective sizing option that meets the
design goals.
The effectiveness of a rainwater harvesting system for managing stormwater runoff depends on
the presence of a consistent and reliable demand that can be used to drawdown the cisterns and
to ensure adequate volume for stormwater retention. The state of Virginia's 2011 design
specification for rainwater harvesting provides specific guidelines for ensuring reliable demand
and offers a robust methodology for cistern sizing based on analysis of the 30-year continuous
rainfall record and anticipated demand scenarios (VA DCR, 2011). The analysis outlined in the
Virginia DCR specification focuses on establishing a runoff reduction credit based on the percent
of runoff volume from storms less than or equal to a target storm of 1" that is retained on site
through the use of rainwater harvesting. VA DCR has developed a Cistern Design Spreadsheet as
a companion to the specification that can be used to estimate the anticipated performance of the
system. The figure below is an example output from the spreadsheet showing the runoff
reduction credit and overflow frequency as a function of cistern size. An optimal cistern size may
be determined based on the location of the "knee" of the curve, commonly perceived as a point
of diminishing return, beyond which incremental additional storage volume has a smaller
incremental effect on stormwater runoff reduction (Foraste and Hirschman, 2010).
10
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Runoff Reduction Credit Chart and Overflow Frequency
5
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* Runoff Reduction Credit Chart
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,000 10,000 12,000 14,000 16,000 18,000 20,
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Cistern Storage Associated with Treatment Volume Credit (gallons)
Source: Foraste and Hirschman (2010). A Methodology for Using Rainwater Harvesting as a Stormwater Management BMP.
Conference Proceedings, 2010 Low Impact Development Conference.
In addition to regional precipitation patterns, Stormwater performance of rainwater harvesting
systems is also heavily dependent on the presence of consistent, year-round demands to
drawdown the cisterns. Both the Virginia and North Carolina rainwater harvesting guidelines
require systems to have a dedicated, year-round use (VA DCR 2011; NC DWQ, 2008). Where
anticipated cistern demand includes seasonal demand, such as irrigation, infiltration or other on-
site practices must be used during non-irrigation months to ensure adequate drawdown rates. In
Virginia, for example, harvesting systems may be combined with other runoff reduction
practices, such as rain gardens, filter strips, or underground infiltration basins, installed
downstream of the cisterns. During periods of low demand, a low level orifice may be used to
"gradually drawdown [tanks] at a specified design rate between storm events" to ensure that the
tanks have adequate volume for upcoming storm events. However, the intent is not for the
system to operate as a detention facility and the typical flows associated with drawdown are far
smaller than those associated with detention facilities (VA DCR, 2011). The water is discharged
to the downstream controls which are engineered to infiltrate the design flow rate. This approach
is particularly useful in areas where irrigation occurs during only part of the year. In these areas,
infiltration practices provide a means of restoring available tank volume during non-irrigation
months in the absence of other water demands (VA DCR, 201 1; Foraste and Hirschman, 2010).
Real-time controls are an emerging technology in the field of rainwater harvesting and
Stormwater management. These systems utilize recently developed hardware and software
solutions to allow for dynamic control of harvesting systems to achieve optimized Stormwater
11
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control benefits. Real-time rainwater harvesting control systems are equipped with internet-
connected logic controllers which are used to monitor the volume of water in the cisterns and
data from weather forecasts in real time to affect the release timing of stored water.
The controller compares the available volume in the cistern to the volume anticipated to be
captured from the forecasted rain event. By releasing water prior to rain events, the system
maximizes runoff capture, thereby reducing discharge volumes, attenuating peak flows, and
enhancing water quality treatment. This is particularly beneficial in combined sewer system
(CSS) watersheds. By releasing stored water prior to the rain event and maximizing storage
volume for an imminent rainfall event, these advanced systems can be used to reduce and
prevent combined sewer overflows (CSOs) from occurring. In non-CSS areas, the release of
water during dry weather helps to attenuate peak flows, thereby reducing erosion potential and
geomorphic impacts on receiving streams. These stormwater benefits are realized with minimal
impact on the supply of harvested water. Through the use of real-time controls, a smaller cistern
volume can be used to realize the same stormwater benefits as a much larger system. Pilot scale
research on real-time control technologies is ongoing and the exact benefits at the site scale have
yet to be quantified.
2.2.2 Operation and Maintenance
As mentioned previously, passive systems rely on consistent, manual water use to deplete the
rain barrel and make volume available for capturing the next rain event. San Francisco
encourages rain barrel owners to use collected rainwater as soon as possible after each rain event
for optimal performance (City and County of San Francisco, 2008). If stormwater management is
of primary concern, it may be beneficial to create additional demands for harvested water outside
of conventional uses such as car washing or lawn irrigation. As part of its rain barrel program,
the City of Los Angeles promotes the creation of rain gardens which can be used to infiltrate
rainwater on residential properties. As part of regular maintenance, owners anticipating
imminent rainfall can empty rain barrels into these areas in the absence of other water demands.
Unlike rain barrels, active harvesting systems are typically sized with some consideration for
stormwater performance during the design phase, eliminating the need for tank emptying as part
of maintenance activities. The primary maintenance considerations for cisterns involve cleaning
of filters and tanks and inspection of equipment, as previously discussed (see the Operation and
Maintenance portion of the Water Conservation section).
2.2.3 Programmatic
State and local codes and regulations typically do not address the use of rain barrels for
stormwater management. However, a number of major cities throughout the country, including
New York, Los Angeles, Portland (Oregon), Philadelphia, and Chicago have implemented
programs to encourage the use of rain barrels and to educate the public on the stormwater
benefits of rainwater harvesting. In some cases, municipalities have invested in the purchase of
rain barrels for distribution to individual homeowners, while others offer rebates for rain barrel
purchases. These programs are generally included in larger green initiatives which are well-
publicized by the sponsoring entity or entities. Such programs help to build understanding and
encourage widespread use of passive harvesting systems.
12
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In the past, many program managers did not know how to account for the water quantity and
quality benefits of rainwater harvesting. Because credit was not granted, use of the practice as a
stormwater management BMP was very limited in many localities. To address this, a number of
states and municipalities have adopted policies and tools to grant the practice credit in order to
put it on a level playing field with other BMPs (Foraste and Hirschman, 2010).
As mentioned previously, the state of Virginia's updated rainwater harvesting design
specification, adopted in March 2011, provides a good example of a method for quantifying the
stormwater runoff volume and pollutant load reduction benefits of harvesting systems (VA DCR,
2011). Historically, many regulations have focused on percent removal as the primary metric for
assigning water quality treatment credit to BMPs. The Virginia specification, however, is
representative of an increasing trend toward the development of stormwater regulations that
recognize the water quality benefits associated with volume reduction. Other states, including
North Carolina, have adopted similar policies, and the Energy Independence and Security Act of
2007 (EISA) - regulating stormwater management at federal facilities - also emphasizes volume
reduction as an effective stormwater management strategy. Other stormwater regulations,
including Total Maximum Daily Load (TMDL) requirements for receiving water bodies, place
additional emphasis on the need for volume reduction.
Rather than focusing solely on percent removal as a metric for assigning water quality treatment
credit for BMPs, these regulations recognize that for a given concentration, the mass of a
pollutant that is discharged to receiving waters is directly related to the amount of volume
discharged. Therefore, a reduction in stormwater volume discharge also corresponds to a
reduction in pollutant loading. As regulators place increasing emphasis on volume reduction,
rainwater harvesting is likely to gain more widespread acceptance as an effective stormwater
management BMP.
It should be noted that while a number of regulators have recognized the importance of volume
reduction in stormwater performance of BMPs, the metrics that have been proposed for
quantifying volume reduction vary. EISA, for example, requires BMPs to be sized for full on-site
retention of runoff generated from the 95* percentile storm event, and many state and MS4
regulations have similar event-based requirements. In some cases, the metric of interest is based
on long-term volume reductions determined from continuous simulation modeling or on a
comparison to pre-development hydrology. Whether specified in terms of event-based or long-
term requirements, procedures for designing a rainwater harvesting system to comply with these
standards are similar and involve the use of a water budget analysis as described in Section 2.2.1.
In response to the increased emphasis on volume reduction in stormwater regulations at the
federal and state levels, many municipalities have recognized the need for dedicated resources to
address stormwater quantity and quality. A number of cities have created stormwater utilities and
changed fee structures to explicitly identify a stormwater fee separate from traditional water
supply and sewer charges. To incentivize on-site stormwater management, several cities
including Louisville and Philadelphia - offer stormwater credits or fee reductions to property
owners who utilize BMPs to reduce runoff volumes. Some municipalities, including New York
City, have also sponsored grant programs to fund pilot projects that demonstrate the efficacy of
using rainwater harvesting to achieve broader goals for CSO reduction and water quality
improvement.
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2.2.4 Predictability
As discussed above, passive systems have little predictability for stormwater control due to their
limited storage volumes and the inability to project when or to what extent storage is available to
accept additional runoff. For active systems, providing consistent demand to ensure regular use
of the stored volume is essential to maximizing the effectiveness of rainwater harvesting as a
stormwater control. Well-designed cistern systems use water budget analyses (as described in
Section 2.2.1) to inform the selection of a tank volume that will optimize stormwater
performance. These analyses consider both precipitation and demand patterns in selecting an
appropriate cistern volume. By enforcing requirements for year-round demand and establishing
well-defined criteria for achieving stormwater credit, state regulations, such as those in Virginia
and North Carolina, can help to make stormwater performance of rainwater harvesting systems
more predictable.
Stormwater Runoff Volume and Pollutant Load Reduction Links to
Recommended Resources
Codes and Policy Documents:
Rainwater Harvesting and Stormwater Management Regulations
Virginia Department of Conservation and Recreation:
Design Specification No. 6: Rainwater Harvesting
North Carolina Department of Water Quality:
Technical Guidance: Stormwater Treatment Credit for Rainwater Harvesting
Guidance Documents
US EPA:
Technical Guidance on Implementing the Stormwater Runoff Requirements for
Federal Projects under Section 438 of the Energy Independence and Security Act
Cabell Brand Center:
Virginia Rainwater Harvesting Manual, 2n Edition
Research Documents:
ASCE Low Impact Development Conference (Foraste and Hirschman):
A Methodology for Using Rainwater Harvesting as a Stormwater Management BMP
14
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2.3 Code and Administration
Although rainwater harvesting has been widely promoted for its water conservation and
stormwater benefits, there has been little consensus among regulators regarding plumbing and
maintenance requirements or the permissible uses of harvested water. As a result, few codes have
been developed to address these issues. The majority of regulations that do exist have been
enacted at the state and local level; the system requirements and level of detail provided in these
codes and ordinances varies from one location to another. This section provides an overview of
the regulatory environment at the federal, state, and local levels with regard to the technical and
operational aspects of rainwater harvesting systems.
2.3.1 Technical
National and International Codes: Until the fall of 2010, neither the national Uniform
Plumbing Code (UPC) nor International Plumbing Code (IPC) directly addressed rainwater
harvesting in their potable or stormwater sections (Kloss, 2008; Traugott, 2007; Ecker, 2007). In
some cases, harvested rainwater was regulated as reclaimed water, which can lead to confusion,
over-burdensome requirements, and discourage or prohibit the use of rainwater harvesting.
In 2010, the International Association of Plumbing and Mechanical Officials (IAPMO) published
the first of its kind Green Plumbing and Mechanical Code Supplement (GPMCS). The
supplement is a separate document from the Uniform Plumbing and Mechanical Codes and
establishes requirements for green building and water efficiency applicable to plumbing and
mechanical systems.
Green Plumbing and Mechanical Code Support
In 2010, the International Association of Plumbing and Mechanical Officials (IAPMO) published the first of its
kind Green Plumbing and Mechanical Code Supplement (GPMCS). The supplement is a separate document
from the Uniform Plumbing and Mechanical Codes and establishes requirements for green building and water
efficiency applicable to plumbing and mechanical systems.
The document was created "to bridge the gap between existing plumbing and mechanical codes and green
building programs" and includes sections on:
Water Efficiency and Conservation
Alternate Water Source Usage
Water Heating Systems
Energy Efficiency for HVAC Systems
Enhanced Environmental Quality for Buildings
The GPMCS also "serves as a repository for provisions that ultimately will be integrated into the Uniform
Codes" (IAPMO, 2010).
According to IAPMO, the entire section of the GPMCS on Alternate Water Source Usage will be included in the
2012 edition of the Uniform Plumbing Code (IAPMO, 2011).
Additional information on the GPMCS can be found at: http://www.iapmo.org/pages/iapmo green.aspx
15
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The purpose of the GPMCS is to "provide a set of technically sound provisions that encourage
sustainable practices and works towards enhancing the design and construction of plumbing and
mechanical systems that result in a positive long-term environmental impact" (IAPMO, 2010).
While making recommendations on a wide range of water efficiency design methods and tactics,
the document does not seek jurisdiction of items addressed in the Supplement: rather, it refers
throughout to the "Authority Having Jurisdiction" and existing codes for matters related to
permitting and approvals.
In addressing "Non-potable Rainwater Catchment Systems", the GPMCS specifically identifies
provisions for collection surfaces, storage structures, drainage, pipe labeling, use of potable
water as a back-up supply (provided by air-gap only), and a wide array of other design and
construction criteria. It also refers to and incorporates information from the ARCSA/ASPE
Rainwater Catchment Design and Installation Standard, a document published in 2008 under a
joint effort by the American Rainwater Catchment Systems Association (ARCSA) and the
American Association of Plumbing Engineers (ASPE).
Also, NSF International has a Task Group on Onsite Residential and Commercial Greywater
Treatment Systems focused on adopting guidelines and standards for the evaluation of on-site
use and reuse systems for greywater, blackwater, rainwater, and stormwater. An initial product
of this work is the NSF/ANSI 350: Onsite Residential and Commercial Reuse Treatment
Systems American national standard. While much of the subject matter is beyond the scope of
this document, it is important to note that certifying an on-site use system for NSF/ANSI 350
also satisfies requirements for leading green building programs such as LEED Building Design
& Construction 2012 Draft Standard and the National Association of Home Builders National
Green Building certification program. Further, examples of fully integrated harvesting and
wastewater treatment system are being built to explore the benefits of combining natural systems
for runoff reduction and onsite treatment. One such example is a system at The Rodale Institute's
Water Purification Eco-Center or WPEC, where a visitor's center incorporates restrooms that use
rainwater for sewage conveyance and constructed wetlands as a safe and eco-friendly alternative
to traditional septic systems (www.rodaleinstitute.org/wpec/home).
Professional Standards: The purpose of the ARCSA/ASPE Rainwater Catchment Design and
Installation Standard is to "assist engineers, designers, plumbers, builders, developers, local
government, and users in safely implementing a rainwater catchment system. It applies to new
rainwater catchment installations, alterations, additions, maintenance, and repairs to existing
installations" (ARCSA/ASPE, 2008). This document discusses the general components of
rainwater harvesting systems and provides guidance on a range of applications, including non-
potable, potable, and fire protection.
Other professional organizations in the construction industry have also started to address
rainwater harvesting as it relates to green building design. For example, the American Society of
Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has added a section on
water efficiency to the latest edition of its ASHRAE GreenGuide, which is intended as an "easy-
to-use reference" for green building design. The introduction of the GPMCS and NSF/ANSI 350,
along with these professional standards, holds promise of significant impact on the design and
construction industries associated with the implementation of harvesting systems, although their
penetration to date in these fields is tough to ascertain. Once adopted by local permitting
16
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authorities on a widespread basis, they should allow for a more uniform and robust design and
installation industry to emerge.
State Guidance and Regulations: At the state level, the amount of regulation for rainwater
harvesting varies widely from state to state. A number of states, including Texas, Georgia, and
Virginia have developed guidance manuals, with several more under development, for rainwater
harvesting and are generally supportive of the practice. In general, state code provisions allow
for more stringent policies than those provided on the federal level, but not less. With the
publication of the GPMCS, states will now have a new benchmark from which to establish their
policies.
In 2006, prior to the publication of the GPMCS, the Texas Water Development Board, along
with other state agencies, created the Texas Rainwater Harvesting Committee to "establish
recommended standards for the domestic use of harvested rainwater, including health and safety
standards [and] to develop standards for collection methods" (TWDB, 2006). This committee
submitted a set of recommendations to the Texas State Legislature which would help to shape
future legislation and create a more formal policy for the collection and use of harvested
rainwater. Other states have followed Texas's lead in addressing the need for rainwater
harvesting legislation. However, progress has been slow; as of 2010, only ten states had policies
or laws specifically addressing rainwater harvesting, and the laws that have been passed often
fail to address key issues such as plumbing requirements and permissible uses of harvested water
(Gold etal, 2010).
With increasing emphasis on green building practices and the call for water and energy
efficiency among those in the construction community, more states are beginning to address the
need for rainwater harvesting legislation. The Illinois State Senate, for example, introduced a bill
in February 2011 that would define "rainwater harvesting distribution system" and "rainwater
harvesting collection system" in the Illinois Plumbing Code and require the Illinois Department
of Health to establish minimum standards for rainwater harvestings systems by 2012 (Illinois
State Senate, 2011). This example is indicative of a growing trend at the state level encouraging
the use and proper regulation of rainwater harvesting systems.
Existing regulations tend to vary widely in scope and focus. Some states, such as Texas, have
focused on rainwater harvesting as a water conservation practice; others, such as North Carolina,
have more structured regulations for rainwater harvesting as a stormwater control measure. More
coordination between state Department of Health agencies, building commissioners and code
organizations, and regional stormwater managers is necessary to aid in the development of more
comprehensive regulations to address all aspects of rainwater harvesting.
Municipal and Local Policies: Municipal and local regulations are more difficult to track, but a
number of examples of rainwater harvesting ordinances or code changes at the municipal level
were discovered in the course of this study. Tucson, Arizona, for example, has passed a law
requiring 50% of a commercial property's irrigation water to be supplied from rainwater
beginning in June 2010. In 2008, Albuquerque-Bernalillo County in New Mexico began
requiring rainwater harvesting to capture at least 85% of rooftop runoff for all new homes
(Kloss, 2008).
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A Broader Look: International Examples of Rainwater Harvesting Regulations
The issue of developing effective rainwater harvesting legislation is not limited to the continental United
States. There are many countries and territories, including the US Virgin Islands, Australia, and Singapore,
that have embraced the practice to encourage conservation, satisfy water demands, or treat stormwater runoff.
Below are examples of the type of progressive legislation enacted in these areas to promote the use of
rainwater harvesting.
St. Thomas, US Virgin Islands: In St. Thomas, developers are required to incorporate rainwater harvesting
systems into all residential site plans in order to obtain a residential building permit. This approach differs
from most U.S. regulations, which are structured to incentivize rainwater harvesting but do not require it.
Harvested water is used mainly for non-potable applications.
City of Salisbury, Australia: The city of Salisbury has implemented a centralized, city-wide harvesting
system linked to the city's existing storm sewer. Runoff is collected and stored centrally, treated, and then
used for groundwater recharge, enabling the city to limit discharges to marine resources while replenishing
the water supply. This approach is somewhat similar to the "storm tunnels" used for temporary detention in
many combined sewer areas in the U.S., but the concept of retaining the stored water for recharge purposes
rather than simple detention is innovative.
Singapore: In Singapore, rooftop runoff is collected from almost all buildings and re-used for non-potable
purposes. Road runoff is also collected into reservoirs and filtered prior to re-use in non-potable applications.
This approach differs from that used in many U.S. communities where runoff from non-roof surfaces is often
restricted due to water quality concerns. These concerns are justified, and the advisability of non-roof
collection depends on the level of treatment and the desired end use.
Additional information on these and other examples of rainwater harvesting practices in international
communities can be found in Stormwater Non-Potable Beneficial Uses and Effects on Urban Infrastructure
(Pitt, et al 2011). Available at:
http://www.iwapublishing.com/template.cfm?name=isbn9781780400365
In addition to encouraging (or even requiring) rainwater harvesting, several local authorities have
also implemented policies outlining requirements for the design, inspection, and approved uses
of harvesting systems. The previously mentioned Memorandum of Understanding passed by the
City and County of San Francisco defines specific roles for the Public Utilities Commission,
Department of Building and Inspection and Department of Public Health with regard to
regulation of rainwater harvesting systems. The document was issued after the City amended its
plumbing code to allow for rainwater harvesting and provides a thorough description of the
technical and permitting requirements for rainwater harvesting in San Francisco (City and
County of San Francisco, 2008). Los Angeles County issued a similar policy in January 2010 "to
establish standardized procedures for the review and approval of plans and specifications" for
rainwater harvesting systems and "to provide guidelines for the approved use and operational
practices for any proposed system prior to implementation" (County of Los Angeles, 2010).
Policies such as these are good examples of a proactive approach to stormwater use regulation.
In the absence of policy, there is often confusion and a tendency to err on the side of
unnecessarily restricting use, rather than encouraging it. Establishing guidelines for the
installation, permitting, and operation of harvesting systems alleviates confusion and can lead to
wider use of the practice, which may be particularly beneficial in arid areas of the western and
southwestern United States.
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2.3.2 Operation and Maintenance
While several states' guidance manuals contain sections describing recommended maintenance
practices, few states or municipalities have enacted laws or codes governing the maintenance of
harvesting systems. The primary reason for this lack of regulation is the lack of available
resources to enforce such regulations.
Many rainwater harvesting policies also fail to provide detailed information on the operation of
rainwater harvesting systems and accepted uses of harvested water. "Harvested stormwater has
most often been used for irrigation purposes, but policies are changing to allow rainwater to be
used for indoor water use where it can meet a significant portion of non-potable water demands"
(Gold et al, 2010). As discussed previously, the AWWA estimated that over 78% of domestic
water use goes to non-potable uses (AWWA, 1999). The Pacific Institute provided a similar
estimate (76%) for office buildings, and data for the CII sector indicate an average of 64% of
water may be attributed to non-potable uses (Pacific Institute, 2003). Water from a municipal
supply or drinking water well is typically treated to drinking water standards, even when it is
used to satisfy non-potable demands.
Development of regulations that match the required level of treatment to the intended use would
allow for the use of harvested rainwater (with minimal on-site treatment) as a viable, low-cost
alternative to the drinking water supply for non-potable uses. In countries such as India,
Germany, and Australia, where rainwater harvesting has gained wide acceptance, additional
efforts have been made to address the need to identify the specific end uses for which use of
harvested water is appropriate. The table below provides an example of a framework used in
Australia to identify the residential and commercial non-potable uses for which harvested water
may be substituted for municipal water. This framework acknowledges differences in required
water quality and treatment depending on development type, end use, and collection surface.
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Key:
Acceptable ^B Possible ("J) Not recommended
t applicable
Amenities Bathroom
Kitchen Food Prep.
Hot Water System
Toilet flushing
Laundry
Irrigation Gar den
Vehicle Gear Washing
Cooling Tower
Pool Top Up Water
Other Process Water
Domestic
(rainwater)
o
o
o
o
o
@
:.
@
Commercial
Rainwater
(from roof
only)
O
o
o
o
o
o
o
o
Q
Stormwater
(roof and
ground)
O
o
o
o
o
o
o
Source: Hauber-Davidson, G. Supplementing Urban Water Supplies Through Industrial and Commercial Rainwater Harvesting
Schemes. Water Conservation Group, Pymble/Sydney NSW, Australia. . (Accessed June 2012).
A similar level of detail is needed in U.S. regulations to remove ambiguity, address barriers to
implementation, and increase the potential benefits of rainwater harvesting as a water
conservation practice.
The City of Portland (Oregon) One and Two Family Dwelling Specialty Code for rainwater
harvesting serves is one example of a code at the local level that addresses this need by
specifying the acceptable uses of harvested rainwater both indoors and outdoors and prescribing
methods for building an approved system that ensures that harvested rainwater stays separate
from potable water (City of Portland, 2001). Similar regulations enacted at the local, state, and
federal levels would promote the use of rainwater harvesting by giving property owners
confidence that their efforts to conserve water resources are both approved and safe.
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Stormwater Pollution and Rainwater Harvesting
In recent years, the potential for contamination of Stormwater runoff with pollutants originating from point
and non-point sources has been a topic of increasing interest for Stormwater engineers and water resource
managers and has played a prominent role in the development of Stormwater regulations designed to protect
public health and receiving water quality. This increased focus on water quality improvement has also
prompted researchers to seek to better understand the sources of pollution which may be found on roofs and
other surfaces.
Understanding the sources of Stormwater pollution is particularly important to the practice of rainwater
harvesting to prevent health risks or unnecessary distribution of pollutants. The body of existing research
contains a number of studies related to the potential for contamination of runoff from commonly used roofing
materials. The table below provides several examples of materials that have the potential to contribute
pollutants to rainwater and recommended, safe end uses for water harvested from these surfaces.
Roofing Material
Asphalt shingles
Galvanized metal
Green roof
Copper flashing,
downspouts
Lead flashing,
solder
Pollutants of Concern
Lead, Mercury
Cadmium, Nickel, Zinc,
Phosphorus
Nutrients, COD
Copper
Lead
Wood shingle Copper, Arsenic, Nutrients
Cement and terra
cotta tiles
Aluminum roofing
Rubber membrane
Lead, Copper, Cadmium,
Bacteria, Asbestos
none
none
Suitable end uses
Contaminants vary by product. Sample water quality prior to use.
Contaminants vary by product. Sample water quality prior to use.
Suitable for irrigation and other non-potable end uses.
Not suitable for human consumption, including drinking
vegetable gardening, or swimming pools.
Not suitable for human consumption, including drinking
vegetable gardening, or swimming pools.
water,
water,
Not recommended for rainwater harvesting.
Not recommended for rainwater harvesting.
All uses
All uses
In areas where rainwater collection from non-roof surfaces is permitted, runoff should be monitored for
contaminants of concern, such as metals, oil, and grease and any site-specific parameters before harvesting is
implemented.
Additional information on Stormwater pollution and rainwater harvesting can be found in the
Recommended Resources listed at the end of this section.
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Codes and Administration Links to Recommended Resources
Codes and Policy Documents:
Plumbing and Mechanical Codes
International Association of Plumbing and Mechanical Officials (IAPMO):
Green Plumbing and Mechanical Code Supplement
International Code Council:
2072 International Plumbing Code
Research Documents:
ASCE Low Impact Development Conference (Gold et al, 2010):
Rainwater Harvesting: Policies, Programs, and Practices for Water Sustainability
US EPA (Kloss, 2007):
Managing Wet Weather with Green Infrastructure: Municipal Handbook on
Rainwater Harvesting
Water Environment Research Foundation (WERF) (Pitt et al. 2011):
Stormwater Non-Potable Beneficial Uses and Effects on Urban Infrastructure
Journal of Irrigation and Drainage Engineering (Clark, et al. 2008):
Roofing Materials' Contributions to Stormwater Runoff Pollution
United States Geological Survey (Van Metre and Mahler, 2003):
The Contribution of Particles From Rooftops to Contaminant Loading to Urban
Streams
2.4 Cost Factors
A perceived lack of economic benefit is often cited as a barrier to more widespread
implementation of rainwater harvesting systems. High upfront costs and easy access to low-cost
municipal or private water sources in much of the United States has led some to discount the
water conservation benefits of Stormwater capture and on-site use. However, recent trends in
water demand and water prices, coupled with the growing number of regulatory and economic
incentives for Stormwater management, indicate a need for a more detailed cost-benefit analysis
of harvesting systems. This section provides a discussion of the factors affecting capital and
maintenance costs of rainwater harvesting systems along with an overview of water rate
structures and the argument for "full cost" pricing of water. The required elements of a detailed
cost-benefit analysis are outlined, including factors affecting the monetary value of each cost or
benefit.
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2.4.1 Technical
Passive systems typically represent a "low-tech" and low cost option for rainwater harvesting
and on-site use. As mentioned previously, a number of cities have distributed rain barrels to
homeowners as part of green initiatives to promote rainwater harvesting while others offer
rebates or coupons for rain barrel purchases. Rain barrels range in price depending on the size
and material; a typical 50-gallon, plastic rain barrel with a spigot and overflow can be purchased
from a hardware store or online retailer for around $70.
Costs for active rainwater harvesting systems vary widely depending on the size and complexity
of the system. For simple systems, which collect water from roof areas and do not require large
media or vortex filters, the storage volume is the primary driver of system cost. Cisterns range in
price depending on the material, size, and shape but costs are typically between $1.50 and $3.00
per gallon of storage, with per gallon costs generally decreasing with increasing tank size.
Additional costs are incurred for filtration, pumps, distribution systems, excavation (if cisterns
are placed underground), distribution plumbing and drainage connections, installation, and other
components. These costs may be significant for large, complicated systems with significant
filtration or distribution requirements: for instance, the installed cost for pumps, controls,
filtration, and treatment can add thousands or tens of thousands to the cost of an active system,
often representing an additional $2 - $5 per gallon of harvesting system capacity.
2.4.2 Operation and Maintenance
Rain barrels typically require little or no maintenance, and any maintenance that is required can
be performed by the homeowner without significant cost.
Maintenance costs for active harvesting systems are generally low for well-designed systems.
Recommended primary routine maintenance and corrective activities and costs associated with
cisterns are listed in Table 2 and 3 below (WERF, 2009). These costs were obtained from the
Water Environment Research Foundation's (WERF) BMP and LID Whole-Life Cost Model
(average hourly labor rates and crew sizes are assumed for each activity). Note that in practice
the frequency of these activities tends to vary. Additional maintenance activities may be needed
depending on the intended use of harvested water and other site-specific conditions.
Table 2: Routine Maintenance Costs for Typical Cistern Systems (WERF*, 2009)
Routine Maintenance Activities
Inspection, Reporting & Information Management
Roof Washing, Cleaning Inflow Filters
M^onths
Between
Events
6
Cost per
Event
Total Cost
ner Year
$ 130 $ 260
6 $ 240 $ 480
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Table 3: Corrective and Infrequent Maintenance Costs for Typical Cistern Systems (WERF*, 2009)
Corrective and Infrequent Maintenance Activities
(Unplanned and/or >3yrs. between events)
Intermittent System Maintenance
(System flush, debris/sediment removal from tank)
Pump Replacement
Years
Between
Events
3
Cost per
Event
$390
Total Cost
per Year
$ 130
5 $ 989 $ 198
*References used by WERF in constructing these tables are identified in the 'References' section at the end of this document.
2.4.3 Programmatic
Among the biggest impediments to the expanded use of rainwater harvesting for water
conservation and stormwater control is the perceived lack of economic benefit and inability to
realize significant return on the substantial upfront cost of system installation, as well as relative
newness of the practice for use in stormwater, which creates uncertainty on how to quantify and
grant credit as a BMP. Researchers have cited the low water cost rates in the United States as
compared to other countries as a major barrier to stormwater reuse (US EPA, 2006). Some
policymakers have sought to address this issue by offering tax breaks and other economic
incentives for rainwater harvesting installations. At the federal level, the American Recovery and
Reinvestment Act (ARRA) of 2009 includes rainwater harvesting as one type of project that is
considered eligible for funding. In addition, a number of states have tax credits, rebates, or grant
programs to help finance rainwater harvesting projects. As mentioned previously, several major
cities also offer credit or fee reductions through stormwater utilities to incentivize stormwater
capture and use. While harvesting systems are typically more expensive than other stormwater
BMPs on a per-gallon-of-runoff-mitigated basis, they offer a water conservation benefit that
other stormwater BMPs do not.
To address the issue of water rates more directly, EPA has advocated "pricing water to
accurately reflect the true costs of providing high quality water" as a means to "maintain
infrastructure and encourage conservation" (USEPA, 2006). This "full cost" pricing would
include the cost to collect, treat, and distribute water and would include capital, operation and
maintenance, and energy costs. The use of full cost pricing "to encourage efficient use and
conservation [of municipal water]," however, must be balanced with the need to provide
"universal access for 'necessity' uses" (NRDC, 2011). To maintain the availability of affordable
water to meet basic needs while encouraging the use of alternative water sources for high
demand applications, some areas have implemented (or are considering) a tiered or block rate
system for water pricing.
A typical block rate pricing structure sets water prices based on each user's water demand
profile. Water demand is divided into blocks based on cumulative water consumption. The first
block - consisting of the first 'X' gallons of water used in a month - is assigned the lowest unit
cost ($/thousand gallons) depending on use or customer type. Any water use beyond the first
block (e.g. greater than 'X' gallons) is assigned to the second block and priced at a higher rate;
rates continue to increase as demand increases and more blocks are added. This type of pricing
structure ensures that affordable water is available to meet basic needs, while high volume users
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are given incentive to seek alternative water sources to offset higher rates for excessive use
(NRDC, 2011).
2.4.4 Predictability
The long-term cost-effectiveness and return on investment (ROI) for rainwater harvesting
systems depend on a number of factors, and few cost-benefit analyses have been published to
date. While a full cost-benefit analysis is beyond the scope of this report, the major issues
requiring consideration in such an analysis are discussed below:
Capital Cost - The initial capital cost represents the primary cost factor associated with installing
a rainwater harvesting system. This initial cost (along with additional costs associated with
maintenance and permitting) is weighed against the present value of future benefits.
Compounding the valuation of up-front investment in harvesting system equipment is the
estimation of the life-cycle of its various components and the system overall. Consistent
representation of life-cycle and mean-time-to-failure data of various wearing components
(pumps, treatment systems, and filtration) would allow for better time-value assessment of up-
front capital costs over the life of the system.
Maintenance Cost - As discussed previously, maintenance costs are incurred for routine and
corrective maintenance performed over the life of the system. These costs are typically minimal
for properly designed systems.
Water Conservation Benefit - According to a 2010 study conducted by the Low Impact
Development Center, the current price of water in the U.S. ranges between $0.70 and $4 per
1,000 gallons with an average of $2.50. The potential for increasing water rates due to increased
demand is often cited as one of the chief drivers for implementing rainwater harvesting,
however, a quantitative financial assessment of water conservation benefits and therefore return
on investment associated with implementing harvesting systems is based on an assumption of
water costs over the life of the system. Coming to some rational projection for the escalation of
water costs in a particular area over a 20 to 30 year period can be a matter of significant
subjectivity. By example, in a 2010 article in the American Water Works Association Journal,
Steve Maxwell cites several examples of rapidly increasing water prices over the last decade and
predicts that this trend will continue and will extend to "more and more regions around the
world" (Maxwell, 2010). Conversely, some public water suppliers project their water costs to
increase at a rate of only 3% per year for the next 25 years. While this is a significant rate
increase over that period, it is far below the double-digit annual increases experienced by some
municipalities over the last 5 years. Clearly the potential for significant water rate increases is
present, however this potential is very hard to characterize.
As a result, it can become difficult or impossible to resolve on water cost escalation factors on
which a financial analysis would need to be based, resulting in an inability to objectively assess
the financial benefits of harvesting as an alternative to centrally supplied water. When
conservatively low escalation rates are applied, there rarely appears to be an economic basis for
investing in harvesting system infrastructure. When reasonably high escalation rates are applied,
systems may be built based on the promise of cost savings, but to date few systems have been
monitored over sufficient time periods to demonstrate that such savings occur.
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Stormwater Management Benefit - In the last decade, an increasing number of municipalities
have implemented stormwater utilities and have established stormwater service fees to property
owners separate from fees already in place for water and sewer services. In introducing this new
fee structure, municipalities seek to increase awareness of the impacts of development on
hydrology and system capacity, and the importance of managing the quantity and quality of
stormwater runoff. To ease demands on downstream infrastructure and mitigate potential impacts
on receiving streams, many municipalities offer credits (or fee reduction) against stormwater
utility fees to property owners for on-site stormwater management. In cities such as Richmond,
VA, cisterns are an approved BMP for reducing runoff quantity and improving runoff quality,
which can result in a stormwater utility fee reduction of as much as 50%. Reductions in
stormwater fees offer a tangible economic benefit for implementation of rainwater harvesting,
which may significantly reduce payback times and lead to more widespread use.
Public Outreach and Sustainability Benefit - Increasing public awareness and advocacy of
environmental programs such as the U.S. Green Building Council's (USGBC) Leadership in
Energy and Environmental Design (LEED) program have created a public relations benefit for
public and private entities that are viewed as environmentally responsible. The LEED program
"promotes sustainable building and design practices through a suite of rating systems" which
identify and award credit for sustainable design choices (USGBC, 2011). Included in the LEED
rating system is a category for Water Efficiency, which includes credit for both stormwater
management and water conservation. Rainwater harvesting systems are well-suited to achieving
these Water Efficiency goals and can be used to achieve multiple LEED certification points. The
USGBC reports that construction of green buildings has a number of tangible benefits to building
owners including positive perception among consumers and potential customers and the ability
to attract tenants and charge increased rental rates (USGBC, 2011).
Energy Use and Environmental Benefit - A significant amount of energy is required to extract,
treat, and distribute water. Data from Mehan (2007) and the California Energy Commission
indicate that "the water sector consumes 3% of the electricity generated in the U.S." and
"decreasing water demand by 1 million gallons can reduce electricity use by nearly 1,500 kWh"
(Kloss, 2008). This reduction in energy use also translates to reduced carbon emissions.
Although difficult to quantify for individual system owners, the value of these benefits may be
considered in a larger scale cost-benefit analysis of rainwater harvesting.
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Cost Factors Links to Recommended Resources
Codes and Policy Documents:
United States Green Building Council (USGBC):
An Introduction to LEED
Guidance Materials
US EPA:
Water and Wastewater Pricing
Research Documents:
Water Environment Research Foundation (WERF):
BMP and LID Whole Life Cost Tools
Duke University (Hicks, 2008)
A Cost-Benefit Analysis of Rainwater Harvesting at Federal Facilities in Arlington
County, Virginia
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3. CONSIDERATIONS REQUIRING ADDITIONAL RESEARCH
Although a significant number of research papers and regulatory policies have been developed
with regard to rainwater harvesting and stormwater reuse, there are several aspects of rainwater
harvesting which may benefit from additional research or policy discussion:
Economics of Rainwater Harvesting - Few cost-benefit analyses of rainwater harvesting systems
have been published to date. An analysis assessing the sensitivity to various parameters,
including demand, cistern size, and water rates could indicate which measures are most likely to
see a quicker payback period, as well as potentially identifying thresholds for each parameter
that make ROI's particularly attractive.
A more comprehensive cost-benefit analysis would consider a number of complicated technical
and socio-economic factors in addition to the primary considerations noted above, including
potential increases in property value and assignment of monetary value to energy savings and
reduced environmental impacts. Such an analysis would need to be conducted for a range of
climate conditions and development types to better inform decisions about Return on Investment
(ROI) and the economic viability of the practice.
Human Health Risks - As discussed previously, many existing regulations already address cross-
connection and backflow prevention procedures to ensure separation of rainwater from the
potable water supply. In most jurisdictions even rain barrels are required to be clearly labeled to
reduce the risks of accidental ingestion. However, when it comes to requirements for treatment
of harvested rainwater before use, little data is available to objectively assess the appropriate
level of treatment needed for a given use and related human exposure. More detailed research
regarding the health risks associated with ingestion of rainwater - and importantly, secondary
exposures such as mists from irrigation system - and how these risks change depending on
factors such as collection area, storage time, and filtration methods, may serve to inform future
policy decisions about the acceptable treatment requirements and uses of harvested water as they
relate to public health.
Regional and Climate Considerations - Rainfall patterns and climate conditions have a
significant impact on the drivers and potential efficacy of rainwater harvesting. In arid areas of
the United States, such as the Southwest, where rainfall occurs during a limited period of the
year, water conservation and flood prevention may be primary drivers for stormwater capture
and on-site use. Communities on the East Coast, however, may realize greater benefit from
reduction of pollutant loads or mitigation of combined sewer overflows. A greater understanding
of the regional factors associated with rainwater harvesting may help to shape policy decisions
and encourage innovation to develop new technologies better suited to the needs and goals of a
particular climate region.
Environmental and Ecological Impacts - Rainwater harvesting systems are an effective means
for on-site stormwater management and are considered a Low Impact Development technique
which helps to match the hydrology of developed land to the pre-development condition.
Widespread use of this practice, however, particularly with indoor use of harvested water, may
significantly alter the water balance of a site as compared to pre-development hydrology.
Additional research is needed to assess the potential for hydrologic and ecological impacts due to
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reductions in infiltration, evapotranspiration, and groundwater recharge associated with on-site
use of harvested stormwater as compared to other stormwater management techniques.
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4. SUMMARY AND RECOMMENDATIONS
This report summarizes the results of a literature review of the research and policy documents
representing the current state of the practice in rainwater harvesting in the areas of water
conservation, stormwater volume and pollutant load reduction, code, and administration and cost
factors.
The key findings from this review and recommendations for future research are summarized
below.
4.1 Findings
While the technical and maintenance aspects of rainwater harvesting in each of these topic areas
have been well documented in state guidance manuals and other available research, relatively
few states have published such manuals and many states have no clearly established regulations
governing rainwater harvesting.
In many areas of the country, significant progress has been made at the municipal level to codify,
permit, and incentivize the use of rainwater harvesting for both water conservation and
stormwater management.
State and local codes addressing rainwater harvesting, while generally similar, tend to vary
somewhat in the level of detail provided, particularly as related to cross-connection/backflow
prevention requirements, treatment requirements, and associated acceptable uses of harvested
water. Regulations addressing the use of rainwater harvesting as a stormwater BMP are generally
better defined and more consistent from place to place.
At present, the most prominent driver for broad implementation of rainwater harvesting appears
to be stormwater runoff and pollutant load reduction due to the regulatory and financial
incentives offered by state environmental agencies and local stormwater utilities.
New control technologies enable the autonomous operation of such systems and provide an
opportunity for improved performance of harvesting systems in stormwater control.
Although the water conservation benefits associated with harvesting systems are significant, the
availability of low-cost centrally-supplied water throughout much of the United States and other
developed countries mitigates the economic benefits associated with water conservation. For
example, a 3,200-gallon cistern designed based on the WERF whole-life cost analysis tool to
r\
collect runoff for a 1-inch storm event on a 5,000 ft roof collection area would have a total life
cycle cost of about $31,000 (net present value). Based solely on water conservation benefit
(assuming an average municipal water cost of $2.50 per 1,000 gallons), this system would
require the tank to fill with rainwater and be completely drawn down over 3,800 times for
payback to be achieved. Note that this payback period is based on the assumption of current
average municipal water rates. As mentioned previously, increases in water rates or the
implementation of block-based pricing may make rainwater harvesting more cost effective.
The absence of detailed, long-term cost-benefit analyses represents a significant gap in available
research related to rainwater harvesting systems.
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4.2 Recommendations
National standards, such as the GPMCS, may provide a guide for defining a minimum standard
of care in the design of rainwater harvesting systems. If adopted by state and local governments,
such codes may help to ensure a level of consistency in local codes across different locations.
A comprehensive cost-benefit analysis conducted for several different climate regions and
development types, considering capital and maintenance costs, water rates, stormwater
regulations and fees, property values, energy savings, and environmental impacts may provide
useful insight into the economic viability of rainwater harvesting practices.
Development of full-cost pricing guidelines of centrally supplied water, including embedded
energy-water attributes, will provide a basis of comparison for alternative water supplies such as
harvesting systems.
More detailed investigations of human exposure paths and associated health risks, climate
factors, and potential ecological impacts of rainwater harvesting are also recommended.
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5. CASE STUDIES
Under the scope of this Task Order, the Project Team conducted a literature review of existing
research and policy documents related to rainwater harvesting, with particular focus on
characterizing the current state of the practice in the areas of: (1) water conservation, (2)
stormwater volume and pollutant load reduction, (3) code and administration considerations, and
(4) cost factors.
Attached to this report are five case studies covering these topic areas that provide examples of
site specific applications of water reuse through stormwater capture. The case studies include
project specific information including: type of demand or use (i.e. irrigation, toilet flushing, etc.),
type of project (i.e. public or private), whether the project is new construction or a retrofit, key
project benefits, and, where available, projected water savings. Figures included in the case
studies illustrate different elements in the rainwater harvesting systems, from above ground
cisterns to underground modular tank systems. The purpose of the case studies is to showcase
how rainwater harvesting can be used to promote sustainability and meet project goals.
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Clark, S.E., K.A. Steele, J. Spicher, C.Y.S. Siu, M.M. Lalor, R. Pitt, J.T. Kirby. Roofing
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.
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