On a walk through neighborhoods between periods of heavy rain, have you ever seen sprinklers running unnecessarily? During our rainy summers, the sight is pretty common, especially in the early mornings. All the extra water can contribute to flooding. The water can also flow across yards, driveways, and sidewalks, picking up nonpoint source pollutants (e.g., pet waste, fertilizer, etc.) along the way. Water and pollutants then flow out of sight into storm drains, making the problem easy to dismiss. However, our storm drains, canals, ditches, and other stormwater drainage systems eventually lead to the waterbodies we treasure, like the St. Lucie River and Indian River Lagoon.

Rain sensors can prevent unnecessary pollution and conserve water

Unnecessarily watering our landscapes during times of abundant rainfall harms our environment and our quality of life by wasting water and polluting our natural waterbodies. Installing rain sensors on automatic irrigation systems is one good way to stop unnecessary irrigation. Rain sensors detect when a certain amount of rain has fallen and send a signal to the irrigation system, telling it to hold off on watering. By not irrigating when the extra water isn’t needed, we save water and prevent further pollution.

How much water can be saved using a rain sensor?

Dr. Michael Dukes and Dr. Dorota Haman of UF offer the following example of potential rain sensor water savings:

As an example, if a system irrigates 1/2 acre of turf and is set to run each zone so that 1/2 inch of water is applied per cycle, one can calculate that 13,576 gallons are being applied over the 1/2 acre of turf per cycle. Assuming water costs $2.00/thousand gallons, the savings will be $27.15 every time the sensor eliminates an irrigation event. Even more importantly, 13,576 gallons that would be lost to deep percolation or runoff will be saved. If this amount is multiplied by the number of substantial rainfalls that occur in the area over one growing season, a significant amount of money and water can be saved. 

Source: https://edis.ifas.ufl.edu/ae221

The state of Florida requires rain sensors or similar technologies

The importance of rain sensors and similar technologies was recognized by the Florida legislature and made a requirement for all automatic landscape irrigation systems. Florida Statute 373.62 requires that “Any person who purchases and installs an automatic landscape irrigation system must properly install, maintain, and operate technology that inhibits or interrupts operation of the system during periods of sufficient moisture.” Rain sensors are available wherever irrigation supplies are sold, and they can be installed by a homeowner or an irrigation professional.

Sensor installation and maintenance are key

Sensors must be properly installed and maintained to function well. During installation, consider the location and the sensor settings. Sometimes people mistakenly install rain sensors underneath building overhangs or other obstructions, where they will not be able to sense any rain events. Rain sensors must be installed in areas where they will receive any rainfall that occurs.

When setting up a rain sensor, UF recommends using the smallest set point possible. Most devices will have a lowest setting of 1/8 inch, which will result in the greatest water savings. In any case, set points of more than 1/4 inch should not be used.

Next, the sensor must be connected to the irrigation controller. Some rain sensors can be connected wirelessly, while others are wired into the control box.

Lastly, sensors do require maintenance and must be tested periodically. Sensor maintenance can be as simple as removing debris or vegetation interfering with sensor function. Sensor function can be tested during normal rainfall events, using a method described by UF researchers, Dr. Michael Dukes and Dr. Dorota Haman, in their publication “Residential Irrigation System Rainfall Shutoff Devices, or Rain Sensors.”

Whenever a licensed contractor installs or performs work on an automatic landscape irrigation system, they are required to test for the correct operation of each rain sensor or other type of irrigation shutoff device (Florida Statute 373.62). If they find the required devices are not installed or not in operating condition, the contractor must install new devices or repair the existing ones before completing other work on the system.

According to research conducted by Dr. Bernard Cardenas-Lailhacar and Dr. Michael Dukes, in areas where water costs exceed $2.00 per thousand gallons, rain sensor costs were recovered in less than a year. The other benefits of rain sensors, in limiting pollution and conserving water, while not as easy to measure, contribute to our quality of life and enjoyment of our rivers and estuary.

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