Treating Water With Less Waste Reverse Osmosis Systems


Treating Water With
Less Waste

Reverse Osmosis Systems	A

EPA

Water Sense

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Treating Water With Less Waste | Reverse Osmosis Systems

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Home or business water treatment systems that use reverse osmosis (RO)
technology at the point where the water is drawn—referred to as point-of-
use systems—are an effective solution for reducing harmful contaminants
from drinking water. However, a typical point-of-use RO system sends
five gallons of water or more down the drain for every gallon of treated
water it produces. RO systems that have earned the U.S. Environmental
Protection Agency's (EPA's) WaterSense® label can reduce water wasted during the RO
treatment process while still providing the water quality that consumers demand. This
document describes the characteristics and benefits of WaterSense labeled RO systems
and provides tips for successful use and maintenance of these systems to maximize
performance and water savings.

Background

Reverse osmosis is the process by which pressure forces water through a membrane that blocks
particles and contaminants while letting clean water pass through. RO creates a stream of treated
water and a stream of concentrated "reject" water (see Figure 1). An RO system can effectively reduce
drinking water contaminants such as lead, volatile organic compounds (VOCs), per- and polyfluoroalkyl
substances (PFAS), arsenic, bacteria, and viruses.

Storage Tank

Treated Water
(Diluted)

Feed Water
Under Pressure

Rejected Water
(Concentrated Contaminants)

Figure 1: Reverse Osmosis Treatment of Water

Reject Water Stream
to Drain

A point-of-use RO system is a water treatment device that is connected to a single fixture (e.g., at the
kitchen sink) that uses the reverse osmosis process described above to remove contaminants from the
water supplied to that fixture (see Figure 2 on page 3). Point-of-use RO systems are typically installed in
residential settings but can also be found in commercial office spaces or kitchens.

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Treating Water With Less Waste | Reverse Osmosis Systems

To Drainpipe

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Restrictor

5th Stage

Post Carbon Filter

4th Stage

RO
Membrane

Feed Water

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Figure 2. Typical Urider-Sink Point-of-Use RO System Configuration

While RO systems can improve water quality, they
can also waste a significant amount of water in the
process. For example, a typical point-of-use RO
system will generate five gallons or more of reject
water for every gallon of treated water it produces. In
recentyears, membrane technology has improved,
and some systems can operate more efficiently,
sending just one or two gallons of water down the
drain for every gallon of treated water produced.

1 Gallon of
Water Treated

3 Gallons of Water Supplied

RO
membrane

2 Gallons of Water Rejected as Waste

1 gallon of treated water
3 gallons of water supplied

¦ 0.33 * 100 = 33% efficiency

RO efficiency ratings are determined by the
percentage of water going into the system that
becomes available to the user as treated water under
typical operating conditions. So a system that sends
two gallons of water down the drain for every gallon of
treated water produced would have an efficiency rating of 33 percent, meaning that 33 percent of the
water that goes into the system becomes available as treated water and 67 percent goes down the drain
(see Figure 3). Therefore, a higher efficiency rating indicates a more efficient system.

Figure 3. Representation of RO System Water Use
and Efficiency

WaterSense Labeled RO Systems

Because the water efficiency levels of point-of-use RO systems varies so much, EPA established a
WaterSense specification to help consumers identify the more efficient models, while ensuring the
water quality that consumers expect. An RO system that bears the WaterSense label is required to have
an efficiency rating of at least 30 percent and meet EPA's performance criteria. Consumers looking for a
new RO system can select WaterSense labeled models that are significantly more water-efficient than a
typical point-of-use RO system. All WaterSense labeled products are independently certified to use less
water and perform as well or better than standard models.

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Treating Water With Less Waste | Reverse Osmosis Systems

A properly designed, installed, and maintained WaterSense labeled RO
system offers many environmental and economic benefits:

• Reduce water waste. While a typical system sends five gallons
of water or more down the drain for every gallon of treated water
it produces, a WaterSense labeled RO system will send no
more than 2.3 gallons of water down the drain for every gallon of
treated water it produces.

• Ensure performance. All WaterSense labeled RO systems
are certified to industry standards and must meet the same
contaminant removal requirements as traditional point-of-use RO
systems.

• Improve water efficiency and save money. While RO systems increase water
use overall compared to using tap water or other filter technologies for water
treatment, selecting a WaterSense labeled RO system to replace an existing RO
system or instead of a typical RO system during a new purchase can reduce water
use for the average household by more than 3,100 gallons of water per year. That's
equal to the amount of water needed to take nearly 200 showers. Reduced water
use can save the average household nearly $50 per year in water and wastewater
costs compared to a traditional point-of-use RO model.

Selecting an RO System

When considering a point-of-use RO system, ensure that the system is the right fit to treat your
household water:

Determine whether RO is the right treatment method to
address your needs. A simple water filter on your tap or
filtered water pitcher may be all you need. If you determine
that RO is right for your home, do not oversize the system. A
point-of-use system should be sufficient for most household
applications.

Understand your RO system options. Some systems have a
tank, typically under the sink, to store treated water, so you
can have it on-demand; tankless RO systems take up less
space, but they might require a booster pump or take a little
longer to fill a glass while the water passes through the RO
membrane. RO systems can be under the sink or countertop
models:

Finding the Right Fit for
Household Water Treatment

The WaterSense Water Treatment
Selection Guide helps you determine
the right water treatment technology
to address your drinking water quality
concerns, as well as your needs for
maintenance and water efficiency.
Review the guide at www.epa.gov/
watersense/point-use-reverse-
osmosis-systems.

Under-sink models are the most common type of point-of-use RO system. They are typically
installed under a kitchen sink and are plumbed in, drawing water from the supply line before it

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Treating Water With Less Waste | Reverse Osmosis Systems

enters the faucet. Most under-sink models direct treated water to a storage tank where it can be
stored and drawn from at any point. Tankless models provide treated water on-demand, typically
with the assistance of a booster pump.

Countertop models are less common, not plumbed in, and may be more appropriate in homes
with temporary residents or spatial limitations. Some countertop systems are fitted directly to the
kitchen faucet outlet and draw water from the faucet via a diverter, while other models can be self-
contained units that draw water from a reservoir that must be filled bythe user.

Make an informed selection. Choose an RO
system that meets your specific treatment
needs based on the following criteria:

• Contaminant Reduction: While RO
is an effective method for removing
several types of contaminants, not all
RO systems remove every possible
contaminant. Manufacturers are
required to provide a performance
data sheet, which includes detailed
information on the systems' efficiency
rating and contaminants the system

is capable of removing. Review the
table on the product packaging and/
or performance data sheet to identify
which contaminants the system has
been certified to remove. Select a
system that has been certified to
remove the specific contaminant(s)
you are looking to treat. Common
contaminants of concern include lead,
arsenic, PFAS, and nitrate.

• Daily production rate (DPR): The DPR

is the amount of treated water an RO
system can produce in a day under
specific test conditions. Ensure that
the DPR rate meets your household
drinking and cooking water needs.

• Water efficiency: Select a WaterSense
labeled RO system to make sure you're
getting one of the most water-efficient
RO systems on the market.

Product Packaging Summary Table

EPA requires all WaterSense labeled RO systems to
include a summary table on product packaging and/
or other point-of-purchase materials that summarizes
the system's water efficiency, daily production rate,
and ability to remove certain priority contaminants.
Consumers can use this table to understand
the system's water use and to confirm which
contaminants the system can remove from their water.
An example summary table is included below.

Water Efficiency and Performance at a Glance

This system has been tested according to NSF/ANSI58 for daily production rate, efficiency, and
contaminant reduction. A system without verified reduction claims for a listed contaminant has
not been verified to remove that contaminant under NSF/ANSI 58.

Daily Production Rate (DPR)

16.4 gallons per day

Efficiency and Water Use

This system has a 32 percent efficiency rating in the
production of treated water. Efficiency rating means
the percentage of the water going into the system
that becomes available to the user as reverse
osmosis treated water. This means that the system
will send 2.1 gallons of water down the drain for
every gallon of treated water it produces.

2.1:1

Waste-to-Treated Water Ratio

Contaminant Reduction

Is this system verified to remove the listed
contaminant?

Contaminant

YES

If yes, what is the
verified reduction?

Total Dissolved Solids (TDS)

97%

Arsenic (Pentavalent) at 50 parts per
billion

94%

Chromium (Hexavalent)

71%

Chromium (Trivalent)

73%

Lead

98%

Nitrate/nitrite

Total Per- and Polyfluoroalkyl
Substances (PFAS)

99%

More Information on System Claims

All contaminants reduced by this system are listed in the performance data sheet. Scan the QR
code or visit (company website) to view the system's performance data sheet.

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Treating Water With Less Waste | Reverse Osmosis Systems

RO System Use and Maintenance

Proper use and maintenance are critical to ensure water quality and effective RO system function. A well-
maintained RO system can last 15 years.

Water Use

Point-of-use RO systems are designed to treat water for drinking and cooking; other water uses within a
home (e.g., clothes washing, toilet flushing, bathing) do not require such high-quality water. Therefore,
using an RO system to treat water for non-consumption purposes can waste more water. To reduce water
waste even further, consider installing a retrofit kit to capture or redirect the reject water created during
the RO treatment process, which can then be used for non-consumption tasks such as laundry, watering
plants, or mopping floors.

Storage Tank

To maintain water quality inside the tank, drain the storage tank periodically—about every two weeks.
Draining the tank also helps the membrane maintain pressure required to remove contaminants. Many
manufacturers also recommend sanitizing your system's storage tank annually. Consider contacting a
service provider to have your system sanitized to reduce the risk of bacteria growth in the system.

Filter and Membrane Replacement

Your system may require maintenance if it shows signs of low
production, low water pressure, or unexpected taste or odor in the
treated water. Over time, soluble and particulate matter will collect on
the membrane surface, reducing system efficiency and contaminant
removal. Membranes and filters should be replaced according to the
manufacturer's product maintenance instructions. In most cases, an
RO system will require pre-filter replacement every six months and RO
membrane replacement every one to five years, depending on local
water quality and use. Filter replacement ensures the system will
continue to perform and helps sustain the life of the RO membrane,
while membrane replacement can ensure the system performs efficiently and produces treated water at
a satisfactory rate and quality.

Automatic Shutoff Device Replacement

Automatic shutoff devices are an important water-saving component installed in WaterSense labeled
and other RO systems with a storage tank. This device shuts off the flow of incoming water when the
storage tank fills to a certain capacity, thereby stopping the treatment process and preventing the tank
from overflowing, thus reducing water waste. A shutoff device can fail or malfunction and periodically
may require replacement. If you notice water continually being discharged to the drain, it may be a sign
that the shutoff device needs to be replaced. Review shutoff replacement instructions as soon as a
malfunction is detected to avoid wasting water and money.

For more information about WaterSense labeled point-of-use RO systems, visitwww.epa.gov/

watersense/point-use-reverse-osmosis-systems.

To learn more about WaterSense, visitwww.epa.gov/watersense.
(866) WTR-SENS (987-7367) j watersense@epa.gov

oEPA

832-F-24-025
November 2024

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