WaterSense Draft Specification for Soil Moisture-Based Irrigation Control Technologies Supporting Statement

WaterSense

WaterSense® Draft Specification for Soil Moisture-Based
Irrigation Control Technologies Supporting Statement

I. Introduction

The U.S. Environmental Protection Agency's (EPA's) WaterSense program released its draft
specification for soil moisture-based irrigation control technologies, hereafter referred to as soil
moisture sensors (SMSs), to further promote and enhance the market for water-efficient
landscape irrigation products.

Residential outdoor water use in the United States accounts for nearly 8 billion gallons1 of water
each day, mainly for landscape irrigation. As much as half of this water is wasted due to
evaporation, wind, or runoff often caused by improper irrigation system design, installation,
maintenance, or scheduling. The most common method used to schedule irrigation is a
manually programmed clock timer that irrigates for a specified amount of time on a preset
schedule programmed by the user, often irrespective of landscape water needs. This draft
specification is the culmination of the EPA's research and coordination with industry since 2006
to develop performance criteria that can effectively identify products that effectively tailor
irrigation schedules to meet landscape water needs based on direct measurements of moisture
in the soil. Once labeled, SMSs, along with other WaterSense labeled irrigation products, will
provide consumers with a variety of smart irrigation technology options that can reduce water
waste outdoors and improve plant health.

A household with an in-ground irrigation system and average outdoor water2 use could save
more than 15,000 gallons of water per year by installing a WaterSense labeled SMS. Replacing
all standard clock-timers in residential irrigation systems across the United States with
WaterSense labeled SMSs could save more than 390 billion gallons of water nationally each
year.

II. Current Status of Soil Moisture-Based Irrigation Controllers

WaterSense estimates there are approximately 28.8 million in-ground irrigation systems
installed in residential landscapes across the United States.3 Less than 10 percent4 of those

1 Based on average per capita water use from Dieter, et. al, 2018. Estimated Use of Water in the United States in
2015, U.S. Geological Survey Circular 1405. U.S. Department of Interior. Table 6, page 23. Average indoor per capita
water use from DeOreo, Mayer, Dziegielewski, and Kiefer, 2016. Residential End Uses of Water, Version 2.

Published by the Water Research Foundation. Page 112.

2 Average outdoor water use per household is 50,500 gallons per year according to the Residential End Uses of
Water, Version 2 (DeOreo, Mayer, Dziegielewski and Kiefer, 2016. Residential End Uses of Water, Version 2.
Published by the Water Research Foundation. Table 6.32, Page 154.)

3 Schein, Letschert, Chan, Chen, Dunham, Fuchs, McNeil, Melody, Strattron, and Williams. 2017. Methodology for
the National Water Savings and Spreadsheet: Indoor Residential and Commercial/Institutional Products, and Outdoor
Residential Products. Lawrence Berkley National Laboratory. Table A-4. Schein et al. describes the detailed technical
approach to WaterSense's stock accounting practice for irrigation products using values available as of the
publication date. As it is the EPA's practice to continuously update its work as data become available, the values
referenced here are for the 2018 analysis, the most recent year available.

4 Ibid.

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WaterSense® Draft Specification for Soil Moisture-Based
Irrigation Control Technologies Supporting Statement

systems are controlled by smart irrigation control technologies,5 leaving a large portion of the
market available for transformation.

As mentioned above, improper irrigation scheduling is a major cause of inefficient irrigation and
water waste. In a majority of existing and newly installed irrigation systems, the irrigation
schedule is controlled by a manual clock timer, where the responsibility of changing the
irrigation schedule to meet landscape water needs lies with the end user or an irrigation
professional. Clock-timer controllers can be a significant source of wasted water, because
irrigation schedules are often set to water at the height of the growing season, and the home or
building owner may not adjust the schedule to reflect seasonal changes, precipitation events or
changes in plant watering needs. For example, plant water requirements decrease in the fall,
but many home or building owners neglect to reset their irrigation schedules to reflect this
change (see Figure 1). Therefore, an irrigation system could be watering in October as if it were
July.

Typical Irrigation Levels and Plant Water Needs

• Average level
at which many
home owners
irrigate

Plant water
requirements

I Potential water
savings

Nov Mar Jul
Seasonal Fluctuation

Mar

Figure 1. Potential Water Savings From Adjusting Irrigation Scheduling Based on

Landscape Water Needs

As an alternative to clock-timer controllers, SMSs make irrigation schedule adjustments by
inhibiting an irrigation event based on a soil moisture reading taken in the landscape. This
allows irrigation to occur only when plants require water Not only does this schedule adjustment
prevent irrigation from occurring after sufficient rain has fallen or if the soil is still saturated from
a previous irrigation event, but SMSs also account for other environmental factors that impact
soil moisture, such as seasonal variation of plant water needs, as well as decreased
evaporation from the soil at the beginning and end of a growing season. By measuring soil
moisture directly and adjusting the irrigation schedule accordingly, this control allows the

5 Smart irrigation control technologies include those that dynamically alter irrigation schedules based on real-time
weather or soil moisture data, including weather-based irrigation controllers and SMSs.

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irrigation applied to better follow the plant water requirement curve displayed in Figure 1. SMSs
and weather-based irrigation controllers together create a suite of smart irrigation control
technologies, and while they function differently, they meet the same goal of efficient irrigation
scheduling and provide consumers with greater options for saving water in the landscape.

WaterSense has actively participated with industry and other stakeholders in the development
of the recently published American Society for Agricultural and Biological Engineers (ASABE)
draft standard ASABE X633 Testing Protocol for Landscape Soil Moisture-Based Control
Technologies. This standard provides a test method for examining the performance of SMSs to
enable or disable an irrigation event at preset or selected soil water values; in other words, it
assesses an SMS's ability to sense moisture in the soil and inhibit an irrigation event when the
moisture exceeds an established threshold. The draft standard forms the basis for the testing
requirements included in this draft specification. WaterSense intends to reference the standard
in its final specification once the final standard is published, anticipated in early 2020.

While all SMSs enable or disable irrigation based on the soil moisture in the landscape, there
are two main differences between products currently on the market. The first difference relates
to the technology used by an SMS to detect soil moisture. Some SMSs use soil water content to
detect soil moisture. These technologies measure a property of the soil (e.g., electrical) that is
related to soil water content. Alternatively, some SMSs detect soil water potential, indirectly
measuring soil moisture. For detailed definitions of these two technologies, please refer to the
ASABEX633 draft standard. The second difference relates to the SMS's connection to the
interface device. SMSs can either be wired to the interface device or wirelessly communicate
with the interface device.

III. WaterSense Draft Specification for Soil-Moisture Based Irrigation Control
Technologies

Scope

This draft specification addresses soil moisture-based irrigation control technologies. It applies
to products that enable or disable an irrigation event based on reading(s) from soil moisture
sensor mechanism(s) (i.e., sensor mechanisms). The EPA is defining this product category as
follows, based on the definitions of the applicable components included in the ASABE X633
Testing Protocol for Landscape Soil Moisture-Based Control Technologies (currently in draft
form);6

• Soil moisture-based irrigation control technology—a sensor mechanism and interface
device that enables or disables an irrigation event at preset or selected soil water values.
These products are commonly known as, and for the purpose of this specification shall
be referred to as, soil moisture sensors (SMSs).

• Sensor mechanism—the portion of the device that contacts the soil and measures
physical properties that are related to water content or potential.

6 WaterSense intends to require soil moisture-based irrigation technologies to be tested in accordance with ASABE
X633 Testing Protocol for Landscape Soil Moisture-Based Control Technologies upon the standard's final publication.
That standard is currently undergoing public comment and final review.

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• Interface device—the portion of the device that either enables/disables irrigation events,
and/or transmits soil water information to a control system for irrigation decision-making.
The interface device could be part of an irrigation controller or can be a separate
component, either integrated into or separate from the sensor mechanism.

This draft specification applies to SMSs that are stand-alone controllers, as well as add-on or
plug-in devices.

A stand-alone controller is an SMS in which the interface device is integrated into the controller.
It includes a single controlling device (i.e., the irrigation controller) and the sensor mechanism(s)
that provide the soil moisture data.

An add-on device is an SMS in which the interface device is separate from the controller (either
a separate component or part of the sensor mechanism). It communicates the sensor
mechanism readings to a base controller (typically a standard clock-timer controller). For
purposes of this specification, add-on devices are defined as those that are designed to work
with multiple brands of base controllers.

A plug-in device is an SMS in which the interface device is separate from the controller (either a
separate component or part of the sensor mechanism). It communicates the sensor mechanism
readings to a base controller (typically a standard clock-timer controller). For purposes of this
specification, plug-in devices are defined as those that are designed to work specifically with
one brand of controller.

Add-on and plug-in devices are included in this specification because they comprise the majority
of the SMS market. In addition, these devices are anticipated to be capable of meeting the
criteria established in the specification.

In providing consistency with the scope and application of the test method to be included in
ASABEX633, this specification is intended to apply to SMSs for use in residential or
commercial landscape irrigation applications. The specification does not apply to:

• On-demand SMSs, defined as technologies that enable irrigation at a lower preset soil
moisture level and disable irrigation at an upper preset soil moisture level.

• Sensor mechanisms alone (i.e., sold without an interface device).

• SMSs intended for use exclusively within agricultural irrigation systems.

Performance Criteria

With the performance criteria for this product category, the EPA aims to label SMSs that can
perform their intended function. As indicated by field and plot studies7, SMSs that can
consistently inhibit irrigation events when a preset moisture level is achieved in the soil save
water.

7 Cardenas and Dukes, Part I, 2016; Cardenas and Dukes, Part II, 2016; Dukes, 2019; The Metropolitan Council,
2019; Torbert et al., 2016; Nautiyal et al., 2014; Grabow et al., 2013; Haley and Dukes, 2012; Cardenas-Lilhacar et
al. 2010; Cardenas-Lilhacar and Dukes, 2010.

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The EPA intends to require SMSs to be tested in accordance with the test method included in
ASABE X633, upon its release. As currently drafted, a replicate of three SMSs per manufacturer
model are each tested at three water depletion levels (20 percent, 40 percent and 60 percent) in
engineered soil (i.e., media) to examine the SMS's response to changes in soil moisture
conditions and ability to consistently enable and disable irrigation events at preset or selected
soil water values.

To generate a set of performance data, the University of Florida tested four models of SMSs
that comprise the majority of the market in accordance with the draft ASABEX633 test method.8
Three replicates of each brand were tested in two soil media and two salinities at each of the
three depletion levels, resulting in four combinations of test conditions per brand for a total of 16
test combinations. WaterSense used these test data to establish the performance criteria
included in this draft specification. From the University of Florida study, WaterSense also
identified several modifications that are aimed to simplify and clarify the test for the purpose of
the specification.

The performance criteria (discussed in more detail below) included in the specification are
intended to evaluate:

• Function—determines whether the SMS has the ability to enable and disable irrigation
at all three depletion levels.

• Precision—a measure of the variability between irrigation enable and disable readings
from three replicate SMSs installed in the same soil media with the same moisture
content. SMS precision is evaluated across the three water depletion levels. Low
variability in the soil moisture readings among different SMSs across a variety of soil
moisture levels ensures that the product can consistently disable an irrigation event at
the same preset moisture threshold.

• Response to change in soil moisture—determines whether the SMS can sense a
change in soil moisture when moisture levels change.

• Function following freeze conditions—evaluates whether the SMS functions after the
sensor mechanism is frozen and thawed to ensure the SMS can operate in regions
where landscapes freeze in the winter.

In addition, consistent with WaterSense's requirements for weather-based irrigation controllers,
the EPA intends to require SMSs (either stand-alone controllers or add-on and plug-in devices
paired with a base controller) to be capable of providing supplemental features (e.g., the ability
to accommodate watering restrictions) to promote greater long-term water savings.

To comply with the EPA's performance requirements, SMSs shall be tested in accordance with
the relevant sections of ASABE X633, as modified in Section 2.1 of the draft specification, and
shall meet the performance requirements outlined in Section 2.2 of the draft specification. SMSs
shall be sampled and selected for testing in accordance with Section 5.1 of ASABEX633 (i.e.,
each test shall consist of three SMSs per manufacturer model randomly selected from a lot of at
least 10 items supplied by the manufacturer).

8 Dukes. 2019. Soil Moisture-Based Irrigation Controller Final Test Report. University of Florida, Institute of Food and
Agricultural Sciences, Agricultural and Biological Engineering Department.

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The subsections below describe the test method modifications and further explain the
performance requirements outlined in the draft specification.

Test Method Modifications

While the EPA fully supports the test method included in ASABE X633, the draft specification
includes three modifications that are intended to clarify testing parameters and streamline the
test procedures:

• Power source: As described in Appendix A of the draft specification, add-on and
plug-in devices shall be connected to a base controller specified by the manufacturer
for the performance test. The draft ASABE X633 standard does not currently specify
how power shall be supplied to the product. However, the EPA is specifying that
these types of products shall be connected to a base controller to supply power. This
addresses potential ambiguity of the power source and also provides assurance that
the add-on or plug-in devices, when connected to a representative and compatible
base controller, have the ability to meet the supplemental capability requirements
included in Section 3.0 of the draft specification.

• Engineered soil media and test water: The ASABEX633 test method, as currently
drafted, requires testing within two test media (i.e. engineered soils): moderately
coarse media (representing sandy loam), and moderately fine media (representing
clay loam). It also requires testing in two salinities in each media: freshwater and
saline water with an electrical conductivity of 3 dS/m (representing reclaimed water
or saline water from other sources). This combination of soils and water salinities
results in testing under four scenarios at each of the three water depletion levels.

The EPA examined test data generated by the University of Florida (see Figure 2)
and found that SMS performance was not statistically different depending upon the
soil media composition (i.e., course vs. fine) or water salinity (i.e., freshwater vs.
saline water).9 Therefore, to reduce the number of tests (from 12 to four) and
associated testing time and costs, the EPA intends to require testing only in the
moderately coarse media (representing sandy loam) with a salinity of 3 dS/m. The
EPA selected sandy loam because it is the more common soil type across the United
States.10 The EPA selected saline water (3 dS/m) instead of freshwater because
users in the past have expressed concern over product performance under saline
conditions.

• Freeze test conditions: ASABE X633 requires the freeze test to be conducted on a
specific depletion level, soil medium and salinity. However, the conditions are
different from the modified test conditions WaterSense is specifying for the

9 The p-value between course and fine media was 0.50 and the p-value between freshwater and saline water (i.e.,
test water) was 0.42. P-values can be used to determine whether one group of data are statistically different from
another group of data. Typically, p-values exceeding 0.05 indicate there is no statistical difference between the two
groups of data.

10 Rodell. 3.3 NCA-LDAS, 2019: NLDAS Soil Texture Types Dataset. NASA/GSFC, Greenbelt, MD, USA, NASA
Goddard Earth Sciences Data and Information Services Center (GES DISC) Accessed: 25 July 2019 at
https://ldas.asfc.nasa.gov/nldas/soils

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performance test. Therefore, the freeze test shall be conducted on the 40 percent
water depletion container using the moderately coarse media after the initial test is
complete. This avoids testing in a new set of soil conditions solely for the purpose of
the freeze test, which would otherwise add undue burden and cost to the
performance testing. As indicated in the University of Florida performance testing,11
neither media type nor salinity (added via water) had an impact on results, so
selecting this combination should provide representative results for the freeze test.

Performance Criteria

To comply with WaterSense draft performance criteria, the EPA intends for SMSs to be tested
in accordance with ASABE X633, as modified in Section 2.1 of the draft specification
(modifications are described above) and meet the following four requirements:

1. Function: Each SMS evaluated shall enable and disable irrigation at each of the three
depletion levels.

This criterion ensures a baseline level of function. Each SMS must be capable of enabling
and disabling irrigation around a soil moisture threshold, as part of the performance test as
described in Section 6 of the draft ASABE X633 standard. If any of the replicate SMSs do
not meet this criterion under any of the test conditions, the test shall be stopped, and the
products do not pass.

2. Precision: The relative average deviation (RAD) of the readings at which the replicate
SMSs enable and disable irrigation, when averaged across all three water depletion levels,
shall be less than or equal to 10 percent.

Because the products are installed and calibrated in the field to enable and disable irrigation
around a threshold moisture level set by the user, precision, not accuracy, determines
whether the products perform and will save water. Therefore, the EPA is specifying RAD as
a performance metric, which assesses whether the three sensors are precise in their
irrigation enable/disable readings under each set of conditions (i.e., combination of soil and
salinity at each depletion level). SMSs with a small RAD have high precision and can
consistently disable an irrigation event across a variety of conditions at the same preset
moisture threshold. The RAD also provides a percentage based on the average deviation
and mean of the readings to normalize the performance metric regardless of the specific
scale a particular brand might use. This allows the precision metric to be compared among
products and to a uniform threshold requirement.

RAD is calculated according to Equations 1 and 2 below.

11 Dukes. 2019. Soil Moisture-Based Irrigation Controller Final Test Report. University of Florida, Institute of Food and
Agricultural Sciences, Agricultural and Biological Engineering Department.

Equation (1)

Average Deviation

Where: x is the mean

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Equation (2)

yV_ jx-x

Average Deviation = 1

Where: x is the mean

Xj is the observation
n is the number of observations

The EPA selected an average RAD of less than 10 percent (RADs averaged across
irrigation enable and disable readings and across all three depletion levels) to reflect the
range of product performance from the University of Florida study.12 Figure 2 shows the
average RAD across all depletion levels and irrigation enable and disable readings for the
four models of SMSs tested by the University of Florida. This graph displays the entire suite
of tests conducted (i.e., two soil media and two salinities), but identifies the one set of
conditions selected by the EPA for this specification. The EPA notes that one product did
not pass the initial irrigation enable/disable test.

While Figure 2 demonstrates that there was a range of RADs observed in the University of
Florida performance testing, field and plot studies that assessed water savings for each of
the three models that functioned properly indicate water savings of at least 30 percent.13
Therefore, WaterSense is proposing in the draft specification a performance criterion
threshold that includes all products that functioned properly in the University of Florida
performance testing.

12 Dukes. 2019. Soil Moisture-Based Irrigation Controller Final Test Report. University of Florida, Institute of Food and
Agricultural and Biological Engineering Department.

13 Cardenas and Dukes, Part I, 2016; Cardenas and Dukes, Part II, 2016; Dukes, 2019; The Metropolitan Council,
2019; Torbert et al., 2016; Nautiyal et al., 2014; Grabow et al., 2013; Haley and Dukes, 2012; Cardenas-Lilhacar et
al. 2010; Cardenas-Lilhacar and Dukes, 2010.

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100%

90%

80%

70%

S 60%

0.01).

This criterion ensures the SMS's ability to respond to a change in soil moisture. Figure 3
shows an example test result for one model of SMS tested in one soil medium, and one
salinity for irrigation enable readings at all three depletion levels. The y-axis represents the
SMS reading for irrigation enable, and the x-axis represents depletion level (one container
for each depletion level at 20, 40, and 60 percent). The three data points at each depletion
level indicate the irrigation enable readings of the three replicate sensors in that container.
This particular example indicates that the sensor reading decreases as depletion increases
(i.e., as the moisture level in the soil decreases). Note that it is possible for a product to
have a positive or negative slope as depletion levels increase, depending on the technology
(soil water potential vs. soil water content, as defined in ASABE X633) and how the SMS
reports its reading. Therefore, the EPA is specifying that the absolute value of the slope
must be greater than zero. A slope of zero would indicate that the product did not adjust its
sensor readings when it was tested in soils with decreased moisture, and that would result
in a horizontal line when the readings are plotted on a graph. These products could still be

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precise in their readings, but might not adequately adjust their readings when the soil
moisture changes. This could affect the point at which the product actually enables/disables
irrigation, depending on the soil moisture content.

The University of Florida test results showed that the absolute values of the slopes of the
tested products ranged from 0.04 to 0.26. Field and plot studies indicate achievable water
savings greater than 30 percent associated with several products that underwent the
testing.14 Therefore, the EPA has determined that, where the absolute value of the slope is
greater than zero in the laboratory test, products should be able to provide water savings in
the field.

25.0

20.0

15.0

o 10.0

5.0

0.0

Sensor Enabled

).2542x + 26.778 .
R2 = 0.9548 '*'1

y = -C

40 60

Depletion Level

• Sensor 1 • Sensor 2 • Sensor 3

• SensorAvg.

. Linear (SensorAvg.]

100

Figure 3. Sample Test Data Demonstrating a Sloped Line in Response to Changes in
Water Depletion Level (Slope = -0.2542)

4. Function following freeze conditions: Each SMS evaluated shall enable and disable
irrigation after the sensor mechanism is placed in a freezer for three days and thawed to
pre-freeze temperature.

The EPA included testing functionality of each SMS after the freeze test to ensure the
products function after one freeze-thaw cycle, as specified in Section 7.2 (with modification)
of ASABE X633. WaterSense is only requiring that the products continue to enable/disable
irrigation after the freeze test. It is not specifying that products meet a specific RAD

14 Cardenas and Dukes, Part I, 2016; Cardenas and Dukes, Part II, 2016; Dukes, 2019; The Metropolitan Council,
2019; Torbert et al., 2016; Nautiyal et al., 2014; Grabow et al., 2013; Haley and Dukes, 2012; Cardenas-Lilhacar et
al. 2010; Cardenas-Lilhacar and Dukes, 2010.

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threshold. Products are recommended to be reconditioned every field season; therefore,
measuring RAD directly after a freeze would not necessarily translate to actual field
conditions.

Supplemental Capability Requirements

To ensure high performing SMSs and to remain consistent with the WaterSense Specification
for Weather-Based Irrigation Controllers, this draft specification includes supplemental capability
requirements for SMSs. The list of supplemental capability requirements was initially developed
for the WaterSense Specification for Weather-Based Irrigation Controllers by water utility
stakeholders who indicated that weather-based controllers should have certain features (in
addition to meeting performance criteria) to promote greater long-term water savings. The EPA
developed the list of supplemental capability requirements that are currently included in Section
4.0 of the WaterSense Specification for Weather-Based Irrigation Controllers in coordination
with a working group consisting of utility and manufacturer representatives. The EPA recently
reviewed the WaterSense Specification for Weather-Based Irrigation Controllers for possible
revision. During that process, WaterSense gathered public comments on that specification.
Stakeholders were generally very positive about the supplemental capability requirements and
did not request any changes.

Though weather-based irrigation controllers and SMSs function differently, both product types
aim to address irrigation scheduling inefficiencies. As such, the EPA intends to promote the
products together as "smart irrigation control technologies." Therefore, the EPA has retained all
of the supplemental features, as appropriate for SMSs, to ensure an equal level of performance
for this product category.

Specifically, stand-alone SMSs and add-on or plug-in devices paired with a compatible base
controller (as described in Appendix A of the draft specification) shall meet the following
requirements in both soil moisture mode and standard mode:

• Be capable of preserving the contents of the irrigation program and sensor mechanism
settings when the power source is lost and without relying on an external battery backup.
This ensures that information regarding the irrigation program and settings are retained
when the power source is lost, and no backup battery is available.

• Be capable of independent, zone-specific programming to successfully manage
landscapes that have multiple areas with various watering requirements that need to be
managed separately.

• Be capable of indicating to the user when it is not receiving sensor mechanism input and
is not adjusting irrigation based on soil moisture content in the landscape (e.g., if there is
a problem with the sensor mechanism that is prohibiting it from enabling or disabling
irrigation).

• Be capable of interfacing with a rainfall device. Rainfall devices are an important
component of an efficient irrigation system in many climate regions. Multiple states have
mandated the inclusion of these devices by law.

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• Be capable of accommodating watering restrictions. With the existence of utility-imposed
watering restrictions, it is important that SMSs, along with their base controllers, if
applicable, are capable of watering efficiently, while complying with these restrictions.

• Include a percent adjust (water budget) feature. This feature allows end users to adjust
water applied to the landscape without changing the detailed settings in the controller's
program.

• Be capable of reverting to a conservative watering schedule (i.e., percent adjust or water
budget feature) if the interface device loses input from the sensor mechanism.

• Be capable of automatically returning to soil-moisture mode if switched to manual mode.
Often products are turned to manual mode for troubleshooting or other reasons and not
returned to soil-moisture mode. This requirement ensures the product will automatically
return to soil-moisture mode within a specified time period as designated by the
manufacturer.

It is important to note that, for add-on and plug-in devices, the majority of these requirements
are likely features of the base controller to which the device will be connected. Since most of the
products currently on the market are add-on devices, the EPA has determined that it is critical to
require manufacturers to identify compatible base controllers that the SMS can be paired with to
meet the supplemental requirements. As described in Section IV of this supporting statement,
WaterSense is not requiring that a WaterSense labeled add-on or plug-in device be tested with
every compatible base controller.

Packaging and Product Documentation Requirements

To ensure that SMSs, as sold, have the capability to provide water efficiency and performance,
the EPA intends to specify packaging and product documentation requirements as part of the
criteria for products to earn the WaterSense label.

Similar to the requirements for weather-based irrigation controllers, stand-alone SMS controllers
shall not be packaged or marked to encourage operation of the controller in non-soil-moisture
mode (i.e., standard mode). Any instruction related to the maintenance of the product shall
direct the user on how to return the controller to soil-moisture mode. The intent of this
requirement is to encourage and ensure the use of the controller in soil-moisture mode.

Add-on and plug-in devices shall not be required to be packaged with the base controller(s) with
which they were tested or have been determined compatible, as specified in Appendix A of the
draft specification. However, the product documentation (e.g., product packaging, user manual,
website, specification sheet) for add-on and plug-in devices shall list each compatible base
controller model. The documentation shall also contain a statement to the effect that the device
is only WaterSense labeled when used in combination with a base controller on the provided
compatibility list. This requirement ensures all supplemental capability requirements are met
when the two products (add-on or plug-in device and base controller) are working together.

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IV.	Testing Configuration and Compatible Base Controller Determination for Add-
on and Plug-in Devices

The EPA intends to require that the manufacturer specify a single base controller model with
which an add-on or plug in device shall be connected and tested. Together, the unit shall be
capable of meeting the requirements of the draft specification, including the supplemental
capability requirements specified in Section 3.0. This requirement allows for consistency with
the weather-based irrigation controller specification and serves as the basis for determining
base controller compatibility, which allows for the retention of all supplemental capability
requirements.

If desired, the manufacturer can work with their licensed certifying body to specify and list
additional base controller models with which the add-on or plug-in device is compatible, if:

•	Together as a unit, the add-on or plug-in device and base controller meet the requirements
of the specification, including the supplemental capability requirements specified in Section
3.0 of the specification; and

•	The compatible base controller communicates with the interface device in the same way as
the base controller with which the add-on or plug-in device was tested (e.g., common wire
interrupt).

The add-on or plug in device is not required to be tested with any additional base controllers
determined to be compatible. As long as the communication mechanism used between
compatible base controllers is the same as the base controller with which the device was tested,
the product should perform well, regardless of the base controller to which it is connected.
Similar to weather-based irrigation controllers, the EPA intends to maintain a list of compatible
base controllers for each add-on or plug-in device on its product registry. This information will
help purchasers and utilities offering rebates ensure that the specific combination of an add-on
or plug-in device and base controller will provide the expected water savings and long-term
performance.

V.	Certification and Labeling

The EPA has established an independent product certification process, described in the
WaterSense Product Certification System. Under this process, products are certified to meet or
exceed applicable WaterSense specifications by accredited licensed certifying bodies.
Manufacturers are authorized by licensed certifying bodies to use the WaterSense label in
conjunction with labeled products.

For add-on and plug-in devices, only the devices certified to meet the requirements of this
specification may bear the WaterSense label. Base controllers with which the add-on or plug-in
devices are tested and/or determined to be compatible shall not bear the WaterSense label.
Product documentation shall indicate that the add-on or plug-in device is only WaterSense
labeled when used in combination with the base controller(s) listed in product documentation
described in Section 4.0 of the draft specification.

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Base controllers that are tested, or determined to be compatible, with an add-on or plug-in
device may bear the promotional label and include language similar to "Look for the
WaterSense labeled [plug-in or add-on device] to improve the water efficiency capabilities of this
controller."

VI.	Other Issues

SMSs have been demonstrated to save significant amounts of water, upwards of 60 percent in
certain applications.15 However, there are numerous outside factors that must be considered
and addressed in order to achieve the intend savings. First, it is important to acknowledge that
the SMS is part of the irrigation system and can only perform as intended if the system is
properly designed, installed and maintained. Second, the controller must be programmed
properly. Third, the end user must monitor water use after SMS installation to determine
whether settings are appropriate or if they can be changed to decrease the amount of irrigation
applied, while still maintaining a healthy landscape.

WaterSense plans to address these issues with a two-pronged approach consisting of
marketing and outreach with stakeholders, including a national network of certified irrigation
professionals. Marketing and outreach strategies will be used to help consumers and utilities
make informed purchasing decisions and necessary irrigation system improvements before
installing these technologies. For example, the EPA intends to publish a technical guide to
SMSs along with the final specification. The EPA also recommends that purchasers of these
products use the services of irrigation professionals who have been certified through a
WaterSense labeled program that focuses on water efficiency and innovative technologies.

VII.	Potential Savings and Cost-Effectiveness

Note: Appendix A provides the assumptions and calculations used to derive these estimates.
Potential Water Savings

SMSs have the potential to save significant amounts of water. WaterSense estimates that 90
percent of the approximate 28.8 million irrigation systems installed in the United States are
controlled by standard, inefficient clock-timer controllers and are candidates for replacement
with smart irrigation control technologies. The EPA estimates that the average household with
an in-ground irrigation system and average-sized residential landscape could save more than
15,000 gallons of water per year by installing WaterSense labeled SMSs. WaterSense
estimates that installing labeled SMSs in residential landscapes across the United States could
save more than 390 billion gallons of water and more than $4.3 billion in water supply and
wastewater costs annually.

15 Cardenas and Dukes, Part I, 2016; Cardenas and Dukes, Part II, 2016; Dukes, 2019; The Metropolitan Council,
2019; Torbert et al., 2016; Nautiyal et al., 2014; Grabow et al., 2013; Haley and Dukes, 2012; Cardenas-Lilhacar et
al. 2010; Cardenas-Lilhacar and Dukes, 2010.

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Cost-Effectiveness

For the purposes of cost savings estimates, the EPA has determined cost-effectiveness in two
ways. First, for a full replacement of an existing clock-timer controller or installation as part of a
new irrigation system, the EPA assumes that the purchase of an SMS consists of either 1) a
sensor mechanism and an irrigation controller for stand-alone products; or 2) in the case of
plug-in or add-on devices, one sensor mechanism, an associated interface device, and a
compatible base controller. Second, the EPA determined the cost-effectiveness for an upgrade
of an existing clock-timer controller, as WaterSense recognizes that add-on or plug-in devices
might be connected to an existing clock-timer controller as an upgrade.

The EPA reviewed the retail prices of SMSs in the marketplace and found the average cost for
full replacement or new installations (i.e., stand-alone controllers or add-on and plug-in SMSs
plus a base controller) to be approximately $250. The EPA determined the cost of add-on or
plug-in devices only (in the case of an upgrade of an existing clock-timer controller) to be
approximately $180. The EPA limited its evaluation of retail prices to SMSs appropriate for
residential or light commercial landscapes, as this corresponds with the assumptions made for
its water savings estimates.

Installing an SMS in conjunction with a residential landscape could save $167 annually for the
average irrigation system, with a payback period of 1.5 years for full replacement or new
systems, or 1.1 years if upgrading an existing clock-timer controller.

VIII. References

Cardenas-Lailhacar and Dukes. 2010. "Precision of Soil Moisture Sensor Irrigation Controllers
under Field Conditions." Agricultural Water Management 97.5 (2010): 666-72. ScienceDirect.
Elsevier B. V., 15 Jan. 2010.

https://www.sciencedirect.com/science/article/pii/S03783774090036317via%3Dihub

Cardenas-Lailhacar, Dukes and Miller. 2010. "Sensor-Based Automation of Irrigation on
Bermudagrass during Dry Weather Conditions." Journal of Irrigation and Drainage Engineering
136.3 (2010): 184-93. ASCE Library. American Society of Civil Engineers, 12 Feb. 2010.
https://ascelibrarv.Org/doi/10.1061 /%28ASCE%29I R. 1943-4774.0000153

Cardenas and Dukes. 2016. "Soil moisture sensor irrigation controllers and reclaimed water;
Part I: Field-plot study." Applied Engineering in Agriculture 32(2):217-224.
https://abe.ufl.edu/facultv/mdukes/pdf/publications/NRES/nres11196 soil-moisture-sensor-
irriqation-controllers-reclaimed-water-part-one.pdf

Cardenas and Dukes. 2016. "Soil Moisture Sensor Irrigation Controllers and Reclaimed Water;
Part II: Residential Evaluation." Applied Engineering in Agriculture 32.2 (2016): 225-34.
https://abe.ufl.edu/facultv/mdukes/pdf/publications/NRES/nres11197 soil-moisture-irriqation-
controllers-reclaimed-water-part-two.pdf

Haley and Dukes. "Validation of Landscape Irrigation Reduction with Soil Moisture Sensor
Irrigation Controllers." Journal of Irrigation and Drainage Engineering 138.2 (2012): 135-44.

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ASCE Library. American Society of Civil Engineers, 23 June 2011.
https://ascelibrarv.ora/doi/10.1061/%28ASCE%29IR. 1943-4774.0000391

Grabow, Ghali, Huffman, Miller, Bowman and Vasanth. "Water Application Efficiency and
Adequacy of ET-Based and Soil Moisture-Based Irrigation Controllers for Turfgrass Irrigation."
Journal of Irrigation and Drainage Engineering 139.2 (2013): 113-23. ASCE Library. American
Society of Civil Engineers, 18 Aug. 2012.

https://ascelibrarv.org/doi/10.1061 /%28ASCE%29I R. 1943-4774.0000528

The Metropolitan Council. "Reducing Water Use on Twin Cities Lawns Through Research
Education and Outreach." University of Minnesota Extension, January 2019.

Nautiyal, Grabow, Huffman, Miller and Bowman. "Residential Irrigation Water Use in the Central
Piedmont of North Carolina. II: Evaluation of Smart Irrigation Technologies." Journal of Irrigation
and Drainage Engineering 141.4 (2015): 04014062. ASCE Library. American Society of Civil
Engineers, 24 Sept. 2014. https://ascelibrarv.org/doi/abs/10.1061/%28ASCE%29IR.1943-
4774.0000820

Torbert, Tolley, Thill, Allen, Dukes and Breder. "Smart Irrigation Controller Demonstration and
Evaluation in Orange County Florida." PDF Report #4227. Waterrf.org. Water Research
Foundation (WRF), 24 June 2016. https://www.waterrf.org/research/proiects/smart-irrigation-
controller-demonstration-and-evaluation-orange-county-florida.

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Appendix A: Calculations and Key Assumptions
Potential Water Savings Calculations

Assumptions:

• 28.82 million detached single-family homes have automatic irrigation systems.16

• 90 percent of the 28.82 million irrigation systems are candidates for installation of
SMSs.17

• Average outdoor water use per household is 50,500 gallons per year.18

• WaterSense has gathered the best available data regarding water savings from SMSs in
field or plot studies, including numerous studies that include SMS brands currently on
the market. Results from these studies indicate a range of water savings from 30 to 83
percent, with an average of 49 percent (weighted by the number of landscapes or plots
from the studies).19 Individual site savings can vary beyond these overall numbers,
depending on the watering habits prior to installing the SMS and local climate. For
example, the majority of these savings studies took place in Florida, where rainfall is
frequent, providing the opportunity for significant water savings. Further, several of the
studies were conducted in controlled plot conditions, and likely inflate water savings
higher than what can be expected in the field. In full consideration of the findings of
these numerous studies, WaterSense estimates seeing overall water savings of at least
30 percent after installation of SMSs.

• The cost of water for irrigation is $11.02 per 1,000 gallons.20 This rate includes the costs
of both water supply and wastewater treatment. It is possible, although uncommon, that
a homeowner could be billed separately for these utility service connections and would
only incur the water supply costs for water used for irrigation.

Equation 1. Annual Individual Irrigation Water Savings From Installing WaterSense labeled SMS
(50,500 gallons/year) x (30 percent savings factor) = 15,150 gallons/year

Equation 2. Candidates for Installation of Labeled SMSs
(28,820,000 irrigation systems) x (90 percent candidates for installation) = 25,900,000 irrigation

systems

16 Schein, Letschert, Chan, Chen, Dunham, Fuchs, McNeil, Melody, Strattron, and Williams. 2017. Methodology for
the National Water Savings and Spreadsheet: Indoor Residential and Commercial/Institutional Products, and Outdoor
Residential Products. Lawrence Berkley National Laboratory. Table A-4. Schein et al. describes the detailed technical
approach to WaterSense's stock accounting practice for irrigation products using values available as of the
publication date. As it is the EPA's practice to continuously update its work as data become available, the values
referenced here are for the 2018 analysis, the most recent year available.

17 Ibid

18 DeOreo, Mayer, Dziegielewski and Kiefer, 2016. Residential End Uses of Water, Version 2. Published by the Water
Research Foundation. Table 6.32, Page 154.

19 Cardenas and Dukes, Part I, 2016; Cardenas and Dukes, Part II, 2016; Dukes, 2019; The Metropolitan Council,
2019; Torbert et al., 2016; Nautiyal et al., 2014; Grabow et al., 2013; Haley and Dukes, 2012; Cardenas-Lilhacar et
al. 2010; Cardenas-Lilhacar and Dukes, 2010.

20 Raftelis Financial Consulting. Water and Wastewater Rate Survey. American Waterworks Association. 2016.

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Equation 3. Annual National Water Savings From Installing WaterSense Labeled SMSs
(25,900,000 candidate irrigation systems) x (15,150 gallons/year) = 393 billion gallons/year

Equation 4. Annual National Cost Savings From Installing WaterSense Labeled SMSs
(393 billion gallons/year) x ($11.02/1,000 gallons) = $4.3 billion

Cost-Effectiveness Calculations

Assumptions:

•	$253 is the average retail price for an SMS as a full replacement of a clock-timer
controller or installation in a new irrigation system (either a stand-alone SMS controller
or an add-on or plug-in device plus a base controller).21

•	$183 is the average retail price for an SMS upgrade to an existing clock-timer controller
(an add-on or plug-in device only).22

Equation 6. Estimated Annual Water Cost Savings From Installing an SMS

(15,150 gallons per year) x ($11.02/1,000 gallons,) = $167 savings per year

Equation 7. Estimated Payback Period for the Average Cost of a SMS (full replacement or new

installation)

($253 product cost + $167 savings per year) = 1.5 years
Equation 8. Estimated Payback Period for the Average Cost of a SMS (upgrade)
($183 product cost + $167 savings per year) -1.1 years

21	Market research based on residential or light commercial models available at the time the draft specification was
released. This includes the price of a stand-alone controller, or for add-on or plug-in devices, the additional cost of a
typical base controller for use in residential irrigation systems.

22	Market research based on residential or light commercial models available at the time the draft specification was
released. This includes the price of an add-on or plug-in device only.

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