How Effective are ET Controllers?

The study noted two interesting points:

  • Irrigation demands typically account for 50% or more of the total water used in many California homes and businesses
  • Improving irrigation efficiency is perhaps the single most important goal for water conservation professionals in the coming years.

The Water-Saving Results Were Mixed

This study definitely demonstrates that irrigation controllers, used in the right circumstances, can save water. It’s also important to understand, however, that “weather-based, smart irrigation controllers, while a valuable tool, are not a ‘magic bullet’ for achieving perfect irrigation control and water savings.” Here’s why:

  • Even the best, most water efficient controller cannot make up for poor irrigation system design, installation, and maintenance
  • On average smart controllers are a moderately effective measure for reducing the amount of water applied by automatic irrigation systems, while maintaining the health, and appearance of landscapes
  • When seeking irrigation water savings, the pre-existing level of excess irrigation at the site is the most important factor to consider
  • The water savings achieved through installation of smart controllers can be maximized by targeting the technology to irrigators with historically high irrigation application rates, not simply customers with high irrigation use
  • The many irrigators who historically apply less than the theoretical irrigation requirement for their landscape are likely to increase their irrigation application rate after installing a smart controller.

accurate weatherset etcontroller smSo even if you install an ET controller, and it uses localized weather data to change the amount of water delivered to your landscape each day, if your irrigation system has been installed and designed improperly, chances are high you’ll see dry, straw-like dead spots in your lawn that will eventually cause you to override the controller and pour on more water than you theoretically should.

The Need for Analytics

ET controller rebates and education programs are a common offering part of many water provider’s conservation initiatives. If the key success factors for ET controllers are:

  • Pre-existing levels of excess irrigation and
  • Historically high irrigation application rates.

…then it follows that water utilities will want to know which of their customers meet these criteria. That’s where analytics can be invaluable.

Using statistical data analysis to review each of your customer’s water usage history and factoring in historical ET and irrigable landscape data (gleaned from GIS or other sources), you can uncover who the over-irrigators are. Targeting your ET controller rebates to these customers first will generate measurable water savings, build momentum for your conservation program, and be a wise use of your conservation dollars.

How Much Water Could be Saved?

The research study measured the following outdoor water savings:

  • Total water savings (1 yr.) = 180,418,500 gals. (330 AF)
  • Smart Controllers (Northern CA) – Saved 47,300 gals. per site. Decrease in usage = 6.1%
  • Smart Controllers (Southern CA) – Saved 30,900 gals. per site Decrease in usage = 5.6%.

The study also found that 959 sites increased their water usage.

A Comprehensive Study

The research paper is very comprehensive and includes a wealth of information about:

  • Different smart controller technologies
  • How various irrigation controller manufacturers’ equipment performed
  • The cost-effectiveness of this type of program
  • Factors that influenced water savings and how those savings persisted over time
  • Customer satisfaction data
  • Best practices and more.


ET controllers can be a powerful water conservation tool. The trick to generating measurable water savings is to target properties that are over-irrigating. Next, you want to inspect their existing irrigation systems to make sure they have been designed and installed correctly. Finally, the customer needs to be educated on how to properly set and use the equipment. This combination of steps will lay the foundation for a successful ET controller program.

A link to the full research paper can be found here: Evaluation of California Weather Based Smart Irrigation Controller Programs (PDF).

This paper was prepared by Peter Mayer, William DeOreo, Matt Hayden, and Renee Davis of Aquacraft, Inc., Erin Caldwell and Tom Miller or the National Research Center, Inc. and Dr. Peter J. Bickel and first published in July 1, 2009.