The Rain Sensor: Is your Rainy Season Hero Alive and Well?

Over here in Southwest Florida, rainy season has officially begun! The unsung hero of the rainy season is none-other than the rain sensor! Rain sensors interrupt your irrigation system controller’s programmed schedule when adequate rainfall has occurred. Thus, saving you the trouble of having to turn your system on and off in-between rain events.

Rain sensors are small devices that are connected to your irrigation system controller, or is hard-wired, and is mounted in an open area where it is exposed to rainfall. Rainfall is measured by water weight, electrical conductivity of water or by expanding disks.

Image of Rain sensor
Rain sensor with expanding disks to measure water.

Expanding disks seem to be used more frequently in rain sensors to measure rainfall. Once rain enters the sensor, the absorptive disks soak up water and expand in proportion to the amount of rainfall and trigger a pressure switch. The amount of rain that will interrupt the irrigation system is determined by adjusting the rain sensor’s cap (A). As long as the disks are swollen, the switch remains open. The vent ring (B) allows the disks to dry out and contract once rainfall has stopped.

To achieve optimal water savings potential, homeowners should adjust the rain sensor’s cap to the smallest point possible, typically 1/8 inch. It is recommended not to exceed a set point of 1/4 inch.

Rain sensors are beneficial in a variety of ways:

  • Conserves water by preventing irrigation during and after recent rain events
  • Reduces wear of your irrigation system & saves money by stopping your system from running when it is not necessary
  • Minimizes presence of disease and weeds by preventing unnecessary irrigation events
  • Protects surface and groundwater by reducing runoff of pollutants into storm drains and groundwater

So beneficial, they are required!

The state of Florida does require (FS. 373.62) a functioning rain sensor, or other rain shutoff device, for every in-ground irrigation system.

Need to check your rain sensor?

Manatee County residents can call the UF/IFAS Manatee County Extension’s Mobile Irrigation Lab to not only inspect your rain sensor, but also evaluate your irrigation system and landscape to save you water! Call (941) 722-4524 x1827 to book a free appointment.

To check your rain sensor:

  1. Manually run an irrigation zone
  2. Spray or pour water onto your rain sensor
  3. See if the zone shuts off on its own or if a rain sensor icon appears on your controller’s screen
  4. If the zone doesn’t shut off or the icon doesn’t appear, you may need to inspect the sensor wiring, cork discs or batteries


Dukes & Haman: Residential Irrigation System Rainfall Shutoff Devices, or Rain Sensors



Maggie Gaughan
Posted: June 14, 2022

Category: Conservation, Florida-Friendly Landscaping, Home Landscapes, Home Management, Lawn, UF/IFAS Extension, Water
Tags: Irrigation, Mobile Irrigation Lab, Rain, Rain Sensor, Save Water, Sprinklers, Water Conservation

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