Rain Gauge vs Rain Sensor, What's the Difference?

Rain Gauge

A rain gauge is used to measure rainfall and/or output from an irrigation system. By checking a rain gauge after each rainfall, you can determine how much it has rained and then reduce your irrigation system’s watering time accordingly. A rain gauge (or small wide-mouth can) can also be used to determine how long to run your sprinklers (see Water Smart, catch can test). Only 1/2 - to 3/4-inch of water per irrigation zone is needed for a healthy lawn.

The most common rain gauges are very inexpensive plastic models available at most garden centers. The gauge is either attached to surface, such as a fence post, or inserted into the ground. A tube collects the water and has measurements marked on the outside for easy reading.

Rain Sensor

A rain sensor is used to prevent an irrigation system from operating during or immediately after a rainfall. Rain causes the sensor to keep the irrigation system turned off during or after sufficient rainfall is measured. Most rain sensors have settings that allow some sort of rain measurement to take place. Settings can usually be adjusted so that a light shower will not affect the system operation. Sensors should be set to shut off the irrigation system when ½- to ¾- inch of rain is received.

Sensors should be mounted high off of the ground in a location that allows the device to collect rainfall without any obstructions from overhangs or trees. Place sensors out of the path of sprinkler spray and never place in full sun or full shade.

Many different models of rain sensors are available at garden centers and through irrigation professionals; sensors can be hard-wired into your system or wireless. Contacting an electrician to install hard-wired sensors is recommended.

Florida law requires any automatic lawn sprinkler system installed after May 1, 1991 to have a rain sensor or switch that will override the irrigation system when adequate rainfall occurs. (See Florida Administrative Code 40C-2.042(2)(a)(5))