Smart Watering With
Soi I Moistu re- Based
Irrigation Controllers
To save water outdoors, many homeowners and businesses with in-ground sprinkler systems
install soil moisture-based irrigation controllers, also known as soil moisture sensors (SMSs).
SMSs detect the amount of moisture in the ground beneath the landscape and prevent
scheduled irrigation when plants don't need water, reducing water waste and promoting
plant health. The U.S. Environmental Protection Agency's (EPA's) WaterSense® program
labels SMSs that have been independently certified to meet performance criteria detailed
in the WaterSense Specification for Soil Moisture-Based Irrigation Controllers. Replacing
a clock-based controller with a WaterSense labeled SMS can reduce outdoor water use by
30 percent, saving an average home thousands of gallons of water annually. This document
summarizes the benefits of WaterSense labeled SMSs, explains how they work, and provides
tips for successful installation and maintenance of these technologies to maximize savings.
Background
At the core of an irrigation system is the controller,
or a timer where irrigation schedules are set,
determining the frequency and amount of water
applied to the landscape. The controller is the key
interface between the irrigation system and end user
in charge of operating that system. Homeowners,
maintenance staff, and irrigation professionals can
control when and how much water is applied to the
landscape by programming their irrigation controllers.
In addition to water savings, WaterSense labeled
SMSs also provide a level of convenience, reducing
the need to change irrigation schedules as the
seasons change. Furthermore, with the growth of app-
based interfaces, some labeled SMSs allow users
to control irrigation right from their mobile devices.
This added convenience allows consumers to track
their irrigation water use, increasing their awareness
of how much water they use outdoors. Additionally,
some labeled models integrate their app-based
software into smart homes' systems, allowing the user
to operate all smart devices from one location.
WaterSense Labeled SMS
A properly designed, installed, and maintained
irrigation system can provide the right amount of
water across a landscape, ensuring water efficiency
and curb appeal. The controller is
the brain behind any good system. In
particular, WaterSense labeled SMSs:
•	Provide a healthy, beautiful
landscape: WaterSense labeled
SMSs help landscapes flourish and remain
healthy by customizing irrigation to only provide
plants the water they need .
•	Save money: WaterSense labeled SMSs help
users reduce overwatering and may lower water
expenses, by only watering when the plants need
it and bypassing the irrigation cycle when water is
sufficient.
•	Reduce water waste and runoff: WaterSense
labeled SMSs avoid unnecessary watering and
decrease the amount of water running off the
landscape, helping to reduce the amount of
pollution flowing to local waterways.
Photo above courtesy of Hunter Industries, Inc.
EPA-832-F-21 -008
PHONE (866) WTR-SENS (987-7367) WEBSITE www.epa.gov/watersense EMAIL watersense@epa.sov March 2021

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• Provide convenience: Properly programmed
SMSs save users the time and effort required to
adjust watering schedules. As app-based products
enter the market, they will provide the added
convenience of monitoring and controlling water
use from mobile devices, whether onsite or from
afar.
How Do WaterSense Labeled SMSs
Work?
WaterSense labeled SMSs prevent normally
scheduled irrigation events from occurring when
adequate moisture conditions exist in the soil. When
the moisture level in the soil is dry enough, irrigation
is allowed to occur; if the moisture level in the soil
is adequate, then the irrigation event is skipped.
An SMS is comprised of a sensor mechanism
and an interface device. The sensor mechanism
stays in contact with the soil and measures the
amount of moisture in the soil. The interface device
communicates the reading from the sensor device to
the controller, which then either allows or prevents
irrigation events.
SMSs come in a variety of models that range in price,
complexity, and capacity. Models range from those
that are intended for small residential landscapes to
those that can control large commercial landscapes'
irrigation. Stand-alone SMSs can replace an existing
controller or be installed in a new irrigation system,
as they provide all scheduling capabilities. Add-
on and plug-in SMSs connect to a base controller
(typically a clock-based controller, but can also be
a weather-based controller). These devices can be
installed to upgrade an existing irrigation controller,
providing the soil moisture-based watering feature to
an existing system. They could also be paired with a
new, compatible base controller and installed in a new
irrigation system.
One thing to know before purchasing SMSs is
whether the sensor mechanism communicates
wirelessly with the control system, or via a wire.
Some SMS models include sensor mechanisms that
are wired to the interface device, while other models
include sensor mechanisms that communicate
wirelessly with the interface device. Another attribute
to note is the number of sensor mechanisms with
which an interface device can communicate. For
small residential SMS models, the interface device
may only communicate with one sensor mechanism.
For models that are intended for use on larger
landscapes, such as large residential or commercial
sites, the interface device may communicate with
multiple sensor mechanisms.
Additional Features Enhance
Performance
WaterSense labeled SMSs (i.e., stand-alone
controllers or plug-in or add-on devices connected to
a compatible base controller) have many capabilities
that offer convenience and flexibility, while promoting
water efficiency. These features include:
Irrigation program information and settings are
retained in the SMS's memory when the power
source is lost and no backup battery is available.
Irrigation can be customized on landscapes
that have multiple zones with various watering
requirements.
•	Alerts tell the user if the controller is not receiving
sensor mechanism input and is not adjusting
irrigation based on soil moisture content in the
landscape.
Because multiple states in certain climate regions
have mandated rain sensors, the SMS must be
able to connect to them.
•	To comply with local utility mandates, SMSs must
be able to accommodate watering restrictions.
•	A water budget feature (also known as "percent
adjust") allows users to adjust the amount of water
applied to the landscape without changing the
detailed settings in the SMS's program.
If the sensor mechanism signal is lost, the SMS
can use the water budget/percent adjust feature.
If the user runs a manual troubleshooting test
cycle, the SMS will automatically return to soil
moisture mode within a specified time period as
designated by the manufacturer.
A searchable list of WaterSense labeled SMSs, their
attributes, and compatible base controllers (where
applicable) is available at https://lookforwatersense.
epa.gov/.
Installing an SMS
Manufacturers include instructions for properly
installing SMSs with the product packaging, and
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many are also available online. Most manufacturers
also provide online training guides and videos on
the installation and operation of their SMSs for
professionals and homeowners to learn more about
installing these products. For help with proper
installation, contact an irrigation professional certified
by a program that has earned the WaterSense label,
which focuses on information on water-efficient
methods and technologies. Find a professional
certifying organization near you for certification
options.
While WaterSense recommends that a certified
irrigation professional install and program SMSs,
many WaterSense labeled SMSs are available
at irrigation supply distributors or online, allowing
homeowners to purchase labeled SMSs and install
them. Installation for these products is typically
straightforward, but remember the following tips:
• Always follow the manufacturer's instructions.
Install the sensor in an area of the landscape that
requires the most frequent irrigation (e.g., turf with
minimal shade). Place the sensor mechanism
in the root zone of the plants. Pay attention to
the instructions regarding whether the sensor
mechanism should be placed in a certain irrigation
zone, as this is product-specific.
Large landscapes may require more than one
sensor mechanism. If so, each one should be
placed in a separate irrigation zone.
Pay special attention to the calibration of the
sensor mechanism and follow manufacturer
instructions. Calibration may vary across brands
and must be conducted properly to realize full
water savings.
If a rain-sensing device is also installed, make
sure that the soil moisture sensor and rain sensor
are wired in series (as opposed to in parallel),
This allows each one to prevent irrigation during
conditions with adequate moisture instead of
requiring both sensors to prevent irrigation at the
same time.
•	After initial installation, closely monitor the
landscape for a few weeks and adjust the settings
if the landscape is too wet or too dry.
•	To realize full savings from an efficient irrigation
schedule, ensure the system is functioning
properly—no overspray onto pavement, broken
sprinklers, or leaks.
Programming for Water Savings
Correctly programming the SMS is necessary to
achieve water savings. As part of the installation
process, many SMS models automatically set the
threshold at which irrigation is allowed/prevented.
The threshold is the point at which the soil holds
the maximum or near maximum amount of water
before irrigation is prevented. After monitoring closely
for several weeks, a user should determine if the
threshold is allowing the landscape to be too wet or
too dry and adjust accordingly. The base irrigation
schedule is equally important. While it may be
tempting to set the irrigation schedule to irrigate each
day and rely on the sensor mechanism to prevent
irrigation if the soil is sufficiently wet, local watering
restrictions need to be adhered to and greater water
savings will be realized if a more typical schedule is
set (e.g., two to three days per week). Note that soil
type should also be considered when programming
Wiring Dual Sensors: SMS and a Rain-Sensing Device (RSD)
INCORRECT	CORRECT
Both sensors are wired in parallel; this does not allow the
sensors to work properly because one sensor may say
"bypass" while the other may say "allow."
NW	
U [Ho]
\\w/
SMS allow
Result: Irrigation
allowed
RSD allow
	"V-
—V.
RSD bypass
xU,/i—i
TJ fcpl
SMS bypass
Result: Irrigation
allowed
SMS allow
Result: Irrigation
allowed
RSD bypass
	%_
SMS bypass
Result: Irrigation
bypassed
In this case, the signal could still travel a complete loop,
and the scheduled irrigation would still occur.
When sensors are wired in series, the signal must travel
a single, complete loop through both sensors, allowing
either sensor to bypass an irrigation cycle.
TT &
\W,
-V.
SMS RSD
allow allow
Result: Irrigation
allowed
SMS RSD
bypass allow
Result: Irrigation
bypassed
SMS RSD
bypass allow
Result: Irrigation
bypassed
r
SMS RSD
bypass bypass
Result: Irrigation
bypassed
In this case, the signal could not travel a complete loop,
and a scheduled irrigation cycle would be bypassed.
Modified from Frank Gaido, University of Florida/international Food and Agriculture Sciences, Pasco County.
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Better Control Is Just One
Piece of the Puzzle
While a WaterSense labeled SMS can help
reduce unnecessary watering, a holistic
approach to landscaping and irrigation is
required to achieve the full potential of water
savings:
Many home irrigation systems operate at a
water pressure that is too high for sprinkler
nozzles and can lead to excessive irrigation
flow rates, misting, fogging, and uneven
coverage. Install WaterSense labeled spray
sprinkler bodies to regulate system pressure
at the sprinkler nozzle.
Utilize microirriaation in flower beds and
other non-turf areas to deliver water directly
to the root zone of plants, where it is needed
most, preventing runoff and reducing
evaporation.
Choose a portion of your yard to be a water-
smart landscape. Plants that are adapted to
your specific climate can reduce the need for
supplemental irrigation.
Group vegetation with similar watering
needs into specific "hydrozones" to reduce
water use and ensure plants get the amount
of water they need by programming your
controller according to each zone's specific
needs.
• Select an irrigation professional certified by
a WaterSense labeled program to assist with
designing, installing, maintaining, or auditing
your system to maximize water efficiency.
the schedule. For example, irrigation runtimes
should be shorter and more frequent in sandy soils
to replace water in the soil without causing drainage
Conversely, in heavier soils, less frequent irrigation
can occur, since the soil holds more water.
Maintaining Savings
Once a WaterSense labeled SMS is installed and
programmed, the controller should effectively deliver
irrigation when the landscape needs it (as determined
based on soil moisture content). However, no
irrigation control system should be installed based
on "set it and forget it." Homeowners, maintenance
staff, or a certified irrigation professional will need
to periodically inspect the landscape to ensure that
the irrigation system is performing properly. This
is especially important after installation. If plants
are unhealthy due to overwatering, irrigation can
be reduced using the water budget feature on the
controller or changing the threshold. Users should
continue to adjust the threshold until they find a
balance that is both water-efficient and healthy for
their plants.
Seasonally, users should follow manufacturer
instructions for winterizing their irrigation system,
including their SMS. Each spring, make sure
to consult the instructions for recalibrating or
reconditioning the sensor mechanism. This ensures
that it is working properly and will allow or prevent
irrigation consistently around the threshold. Like
other irrigation system components, SMSs need to
be replaced as recommended by the manufacturer,
typically within five to seven years.
For more information about WaterSense labeled
SMSs, visit https://www.epa.aov/watersense/soil-
moisture-based-control-technoloaies
For more information about
smart outdoor water use, visit
httDs://www.eDa.cov/watersense/outdoors.
Photo above courtesy of Michael Dukes, University of Florida
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