One of the newest developments to hit the light commercial and residential irrigation markets are ET, weather-based, “smart controllers”.

The technology was originally developed for large-scale agricultural irrigation systems and has slowly filtered its way down through golf courses and larger commercial projects to the average consumer. This has been in part due to the high demand for water-saving products.

ET stands for evaporation/transpiration and is a measurement of the amount of moisture lost from the soil each day due to evaporation and transpiration (through, or used, by plants). Smart controllers use five pieces of current weather information (wind speed, solar radiation, humidity, temperature, and rainfall) to calculate the ET rate for each zone in an irrigation system and then adjust the run time daily to replace the lost moisture.

With a conventional irrigation time clock we set the day and time (water window) we want the system to run and then set each zone for the length of time we think is appropriate. When programming an ET-based controller the user sets the water window but instead of setting the zone run times, we provide the controller with basic information about the irrigation system for each zone, the type of plants we are watering, and the environmental factors for each zone.

Based upon this information, and the calculated ET rate, the controller determines the precise run time for every zone. If we have cool, overcast, high humidity days the system will run less than if we had bright skies, high temperatures, and dry windy days. “Smart controllers” typically reduce irrigation water consumption by 30% to 60% and take all of the guesswork out of setting your irrigation controller.