ET Controllers, Facts and Figures

Conventional controllers are by far the most common way to regulate irrigation applications. The Marina Coast Water District encourages the replacement of simple, conventional irrigation controllers with evapotranspiration (ET)-based controllers for the following reasons:

• It is estimated that approx. 50% of residential water use goes towards outdoor use including landscaping.  It is estimated that 15 - 40% of this water is not required for optimum plant growth and is therefore wasted.
• Simple, conventional controllers do not adjust the amount of water applied automatically to compensate for changing weather or periods of rainfall.  Due to the high cost and effort required to frequently adjust the conventional controllers; these adjustments are often not made.
• The evapotranspiration rate of landscape microclimates differs greatly and therefore so does the water requirement of each microclimate.  Accurate calculations of the water required in each microclimate are laborious due to the various factors such as plant type, soil type, slope, sun exposure, and landscape density. All these factors should be included in any calculation of water requirement or sprinkler run time.
• Irrigation managers often over-water to compensate for unexpected dry periods or to meet the higher water requirements of an irrigation system with poor uniformity. Both of these situations lead to costly damage to the landscape.
• Over-watering leads to runoff and pollution, or gravitational water loss through the soil profile.
• Over-watering or the lack of sufficient available water causes diseases, plant stress and plant loss.
• The greatest portion of inefficiency in irrigation systems is due to improper scheduling, one of the easiest factors irrigation managers can change by installing new ET-based irrigation controllers.
• Average historical ET values may differ significantly from actual ET. Older historical ET controllers do not take into consideration the immediate weather and make-up water required after periods of high ET.

ET controllers can address the many problems of conventional controllers that contribute to water waste. The benefits are:

• ET controllers directly address the leading cause of water waste in landscapes, the lack of frequent adjustments to duration and frequency.
• ET controllers can assist the manager by calculating the proper application duration and frequency daily based on the many factors that effect evapotranspiration and gravitational water loss. This commonly saves 15-40% in irrigation water use.
• The high water savings and therefore fast payback period justify the investment to upgrade controllers.
• Runoff due to over watering can be reduced by more than 50% or almost eliminated.

There are some important considerations one must make when considering the retrofitting to an ET controller.

• Irrigation scheduling is only one of four important factors affecting the amount of water applied to landscaping.  The others are distribution uniformity, irrigation system leaks, and the water need of the landscape plants.
• There is a higher initial cost and often a data service fee for ET controllers. The high water savings and fast payback period of ET controllers often justifies the additional expense.
• Plant health is often improved due to proper water application based on soil type and evapotranspiration of the landscape.
• There is some initial set-up time and an adjustment period that follows the installation of ET controllers. Site data must be collected and entered into the controller software.

Appropriate sites for the retrofitting of ET controllers are:

1. Dedicated commercial, industrial, and institutional landscape sites.
2. Mixed use commercial sites.
3. Dedicated and mixed use multi-family sites.
4. Single family residential sites.

Not all ET controllers have the same function nor do they function or perform the same.

To learn more about the features and performance of the top ET controllers, visit the Irrigation Association's Smart Water Application Technologies site.