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Irrigation Efficiency
People tend to use fixed run-times (15, 20, 25 minutes, etc.) when setting their irrigation controllers and typically turn the controllers on in the spring and off in the fall. Irrigation controllers are perfect for part-time residents who aren’t around to monitor and change their run times. They are also great for large properties with a lot of grass or for homeowners who don’t want to hire a landscaper. But even if the run-times are set perfectly in the summer, the amount of water wasted during the cooler spring and fall is considerable.

What is ET?
ET is short for evapotranspiration, which is a combination of:
  • Evaporation from soil and exposed surfaces.
  • Transpiration, the process by which moisture is carried from the plant roots and released through leaves - the evaporation of water from plant leaves.

About ET Controllers

An ET controller, also known as a weather-based controller or smart controller, is simply a controller similar to existing controllers for irrigation (sprinkler) systems. ET controllers deliver only the amount of water needed to a specific plant or area based on input variables such as plant type, soil, slope, and weather.

Outsmart the Seasons
The following is a summary of the amount of over-watering associated with typical run-times compared to ET run-times for turf during the spring, summer, and fall of 2003:
Typical Sprinkler Run-Times
Percent Over-Watered Compared to ET-Based Run-Times
15 minutes
20 minutes
25 minutes
30 minutes

Different ET controller systems use slightly different estimates of ET. ET can be estimated from weather variables including temperature, humidity, and wind. The DWP maintains a local weather monitoring station that is part of the California Irrigation Management Information System (CIMIS) that records weather data and transmits it daily. By monitoring the data, Bear Valley residents can use their controller to replace the exact amount of water lost on a day-to-day basis resulting in extremely efficient irrigation.

This is the station you are looking for if you use the CIMIS station website:
Number Name Region
199 Big Bear Lake San Bernardino

The following chart shows the ETo rate for Big Bear Lake based on the Model Water Efficiency Landscape Ordinance. 
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total
1.8 2.6 4.6 6.0 7.0 7.6 8.1 7.4 5.4 4.1 2.4 1.8 58.6

Irrigation Maintenance
As a general rule of thumb, irrigation systems should be inspected seasonally. Check out the Sprinkler Spruce-Up page for instructions. 

Additional Information

If you would like more information about ET or any of the DWP’s water conservation programs, please contact the Conservation Department.