According to a recent study sponsored by the California Landscape Contractors Association’s Water Bill Task Force, California could save 100,000 acre-feet of water per year if irrigation of large landscapes did not exceed an efficiency rate of 100 percent of reference evapotranspiration.
“100,000 acre-feet is a tremendous amount of saved water,” says CLCA president Jon Singley. “It would provide for the water needs of 200,000 averaged-sized families for a one-year period.”
Reference evapotranspiration (ETo) is an estimate of the water needed to irrigate cool-season grass in a specific geographic location. Irrigation in excess of 100 percent of ETo is widely viewed as wasteful, no matter what the style or design of the landscape.
STUDY OBJECTIVES. The study was undertaken by John Whitcomb, PhD., an expert in water demand analysis. It had the following three objectives:
1) Deteremine current water use on California’s commercial, industrial and institutional (CII) landscapes;
2) Estimate this use as a percentage of ETo; and
3) Estimate potential water savings if the landscapes were irrigated at no more than the 100 percent level.
Using published information fromt eh California Department of Water Resources, the report concluded that the state’s CII sites use 1.17 million acre-feet of water per year or 13.3 percent of California’s urban water use. Of those sites, those which have a dedicated landscape meter use .64 million acre-feet of water per year or 7.3 percent of the state’s urban water use. (A dedicated landscape meter is a water meter that measures landscape use and not other uses, such as indoor applications.)
Using actual water use data from 449 large landscapes in California, the study estimated that California’s large landscapes are currently being irrigated at an average of 93 percent of ETo.
“This percentage is better than we expected,” says Singley. “Several of our members had predicted it would be closer to 120 percent.”
However, despite these averages, the study showed that 50 percent of the state’s large landcapes are irrigated at more than 100 percent.
“This is where the opportunity is to conserve landscape water,” Singley noted.
INTERESTED DATA ON TURF. The study concluded that the variation at which sites are irrigated results from a variety of factors. However, sites with a high percentage of turfgrass, which is usually thought of as the most water-intensive plant, did not exceed the 100-percent threshold more often or to a greater degree than sites with other types of plants. According to the study, “this evidence suggests that the conversion from turf to other irrigated plant materials (e.g., shrubs) does not necessarily convert into lower water use given current (inefficient) water management practices.”
“This illustrates what many green industry professionals have long been saying, that better water management is far more important than planting ‘politically correct’ plants,” says Singley.
If water waste, definted as irrigation in excess of 100 percent of ETo, were eliminated, 100,000 acre-feet of water would be saved per year on the large CII sites with dedicated meters. 133,000 acre-feet per year would be saved between now and 2020 if future population increase estimates are taken into account. Far more water would be saved if large CII sites with mixed (non-dedicated) meters were figured into the calculations.
“This study illustrates so well that a tremendous amount of water can be saved if we eliminate waste,” Singley says. “The most efficient way to do that is to create rate structures for landscape water use that discourage waste and reward efficiency. The installation of dedicated landscape meters would be necessary to encourage water budgeting on all large CII sites, but this is easy and cheap to do. Unfortunately, though, not many water agencies have landscape conservation rate structures in place at the present time.”
BENEFITS OF AB 607 ILLUSTRATED. The Water Bill Task Force was chaired by Barbara Alvarez of Golden State Landscaping in San Dimas, Calif. Task force member Scott McGilvray of Jensen Corp. Landscape Contractors in Cupertino worked with CLCA Assistant Executive Director Larry Rohlfes to define the study objectives.
The task force commissioned the study to show how much ater could be saved by Assembly Bill 607. This proposed legislation, sponsored by CLCA, would have encouraged local communities and water districts to meet landscape water conservation goals by adopting rate structures to reward efficient irrigation practices. Unfortunately, the bill was unable to hurdle the Assembly Appropriations Committee last summer and it died in January 2004.
“The bill may be a few years ahead of its time, but I’m convinced that one day we’ll dust it off and turn a version of it into law,” Alvarez says.
This article appeared in the February 2004 edition of the California Landscape Contractor’s Association newsletter The Cutting Edge. Visit www.clca.org for more information.