SMART IRRIGATION SECTION: Case Study No. 1: Irrigating in Irvine Ranch

Home landscape water use can consume up to 59 to 67 percent of total home water demand, according to the American Water Works Association Research Foundation report “Residential End Uses of Water.” What is the value of a home’s landscape and how much water should it use? While there is no precise answer, attractive landscapes have been shown to increase property values from 7.28 to 15 percent. How much water a home landscape needs depends on its soil, sun and shade exposure, plant types, irrigation system and local climate. 

Landscape and irrigation contractors can help their clients save water with a combination of low-tech and high-tech solutions. The two techniques described here helped reduce home and commercial landscape water use in Irvine, Calif., by 50 percent from 1991 to 1999, saving consumers $28 million.

LOW-TECH SOLUTION: SOIL PROBES. Landscape and irrigation contractors and university researchers use soil probes to determine soil-moisture levels. Using a soil probe is as easy as inserting it into the ground, pulling it out and then feeling and seeing the soil in it. To test the water-saving potential of this simple device, the Irvine Ranch Water District conducted a voluntary test of 90 homes.

Residents were instructed to use the probes as follows:
1. Turn irrigation systems off.
2. Push the probe into the ground (where turf, shrubs, trees and groundcovers are planted).
3. Pull out the probe and observe and feel the soil.
4. If the soil is wet or moist, do not water.
5. If the soil is dry, turn water on (using the probe to determine that water is applied only within the turf root zone).
6. Repeat the process before the next watering.
 
The first test group of 30 homes was monitored in the summer of 1997 (July through September). The second test group of 30 homes was monitored in the spring of 1998 (April through June) and the third in the fall of 1999 (October through December). The test homes were compared with neighboring non-test homes (the control group) on the same streets. The water savings were measured against the previous year’s water use for all test and control homes. The water savings for the test homes over control-group homes were beyond agency expectations – 69 percent in the spring, 24 percent in the summer and 16 percent in the fall.
 
The $12 probe cost was recovered in average home water savings within each three-month test period regardless of the season. The probe’s cost-effectiveness combined with positive customer response makes it a simple and effective water conservation tool that landscape and irrigation professionals can encourage their customers to use. Many contractors have given probes away as promotions to customers who purchase irrigation systems or sign up for irrigation maintenance programs.

HIGH-TECH SOLUTION: ET IRRIGATION CONTROLLERS. How much water plants require depends on the type of plant and its evapotranspiration (ET) rate. ET is the total amount of water lost from the soil through evaporation or used by plants to take in nutrients and control temperature. For healthy growth a plant needs only the amount of water the ET rate provides. Most plants suffer when they receive more water. Applying the right amount of water, based on the local weather and the plant’s actual need, is the key to using water efficiently.
 
Computing and setting landscape irrigation time based on weather changes is a complicated, time-consuming and never-ending task. However, new irrigation scheduling technology can change how contractors install systems so their customers can save water.
 
A wireless technology transmits local weather-station data each week directly to homes equipped with ET-receiving irrigation controllers, setting new and efficient irrigation schedules. The technology was tested in a one-year study of 120 homes in Orange County, Calif., that was sponsored by the Metropolitan Water District, the Municipal Water District of Orange County and the Irvine Ranch Water District. The study evaluated the controllers’ ability to perform three functions – set efficient irrigation schedules based on local weather, soil type, plant type, irrigation system output and plant root depth; change irrigation schedules as the weather changes via a broadcast received by the controller; and eliminate the need for users to set, change or try to reprogram the controllers to meet plant requirements as the weather changes.
 
The study showed that the ET irrigation control technology resulted in home landscape water savings of 17 to 25 percent and indicated that water savings increased dramatically as the size of the landscape increased.
 
The study indicated that homes using moderate amounts of water for landscapes could save 57 gallons of water per day. This translates into an average annual savings of at least 20,000 gallons of water saved per home.
 
The study found these additional benefits of ET irrigation control technology:

• All test-home residents found the controller to be convenient because they did not have to manually set, change or reprogram irrigation times.
• The average annual water cost savings, at $114, was greater than the yearly ET weather data broadcast signal fee of $48.
• Homeowners reported their landscapes looked as good as or better than they did prior to the use of the ET irrigation control technology.
• The capability of the controller to be set for the soil-infiltration rate, slope and sprinkler output greatly reduces the potential for water runoff.
• The technology can be set to specific or staggered times to assist with local supply shortages and/or occasions when local water use peaks.
• The technology can send a reduced percentage signal prescribed during drought periods. (For instance, if an area needs to reduce water use by 20 percent, the broadcast system can send an ET signal that is 20 percent lower across that part of the customer base outfitted with the technology.)

The author has more than 20 years of experience in water management. He is director of conservation alliances, HydroPoint Data Systems, and previously was the Irvine Ranch Water District conservation coordinator and a University of California cooperative extension specialist. This case study was reprinted from the book Water Right by the International Turf Producers Foundation.