Culinary Water Waste in Landscape
Earl Jackson, Salt Lake County Agent, Utah State Extension Services
Utah is:
- 3rd most urban state in the nation
- 2nd driest state
- 2nd state in per capita water use
- #1 hobby is gardening
- Passion for green Jello and grass
What is a ‘water check’?
A water check is a modified audit of a landscape and irrigation system following the methods and terminology of the National Irrigation Association.
Residential Sites Evaluated
- 2,807 residential properties evaluated
- 48 cities
- 6 counties
Large Water Use Sites Evaluated
To date, the irrigation systems of 83 parks, schools, churches, apartment complexes and public facilities have been evaluated.
Inefficient Sprinkler Systems
- The average distribution uniformity (efficiency) of both fixed popup heads and the larger rotor heads on residential properties is only 56 percent efficient. A properly installed irrigation system should be a minimum of 70 percent efficient.
- The average residential water pressure measured during the day at a sprinkler head is 51 pounds per square inch (psi). This is too high for the typical fixed popup sprinkler head and increases misting and evaporation. Nearly all fixed popup sprinkler heads are manufactured for use between 15 and 30 psi of water pressure. On the other hand, the large rotor sprinkler heads usually work at pressures greater than 70 psi.
- Precipitation rate is a measure of how much water is emitted from a sprinkler head. It is measured either in inches of water per hours (like a rain storm) or in gallons per minute. The average residential fixed popup head puts out 1.4 inches of water per hour. Most soils cannot absorb water at this fast of an application rate. Sprinklers apply water faster than a very heavy rain storm (0.5 inches/hour). You should determine how long it takes each zone of your sprinkler system to put out 1/2 inch of water. If you have an average system output of 1.4 inches/hour, run your sprinkler for 21 minutes on sandy or loam soil to put out 1/2 inch of water. If you have a clay soil, split the 21 minutes into three cycles of 7 minutes applied about one hour apart. Remember that the larger rotor type heads on the average have a precipitation rate about half (0.7 inches per hour) the rate of fixed popup heads.
Poor Watering Habits
A shallow watering every day is about the worst thing you can do for your lawn because it keeps the roots short. Then during the hot days of July and August, one needs to water every day to keep the lawn from going dormant. The average residential lawn has a root system only 5.7 inches deep. With a uniform soil and proper irrigation, a bluegrass lawn should have a root system 12 to 18 inches deep. The deeper the root system the more days you can wait between irrigations. Remember to water deep, twice a week (apply at least 1/2 inch of water each irrigation and let the soil surface dry between waterings).
Proposed Watering Schedule
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Culinary Water Waste at Residential Sites
Along the Wasatch Front, a green healthy lawn requires 25 inches of water either from rain or irrigation, evenly spread out during the growing season which is usually April through about October 15th. Applications of irrigation water should follow the above irrigation schedule. The standard is known as the turf water requirement (called ET for Evapo Transpiration), which is 24.7 inches of water or 15.42 gallons per square foot per season. The average hose connection has a pressure of 73 psi with a hose output of 8.2 gallons per minute. If water infiltrated all soils as fast as loose sand, one could use the season water total on a square foot of grass in 2 minutes.
After four years of drought conditions in Utah during 1987 to 1990, we had normal to wet years without any lawn watering restrictions. The average resident applied nearly 57 inches of water to his/her lawn during 1996 and 1997. This is 224 percent of the standard water requirement. In 1999 another drought cycle started and 2002 will be the fourth year of this cycle. During the last three years, the average resident in this water check program (2,807) used 50 inches of water or 201 percent of the standard. This is less water used than during the wet cycle but still very wasteful. This means that on the average, we use twice as much water as the landscape requires for the season.
Residential Water Savings
- The percentage of water saved after a residential water check varies by the customer group, the year of the water check and the location along the Wastach Front. The year following a water check, the group served by Salt Lake City Public Utilities reduced their water use by 12.3 percent.
- Those having a water check during 1999 served by the retail section of Jordan Valley Water Conservancy District reduced their water use 28 percent during 2000.
- Those residents who took out part of their front lawn and put in perennial plants or shrubs ( a xeriscape type landscape) reduced their water use by 19 percent on average.
- The average lot size in this study is 13,589 square feet (0.31 acres). The average irrigated landscape size is 7,894 square feet (0.19 acres). On the average, 62 percent of a typical lot is landscaped.
- The average number of people per household is 3.4 both winter and summer. The average household used 250,490 gallons of water a year. This amounts to 9.2 acre-inches per year. Therefore, the average family of four requires 10.9 acre-inches of culinary water per year. The average per capita water use is 202 gallons of water per person per day. Of this amount, we use 75 gallons indoors and 127 gallons per day per person outdoors. This means that for watering our landscape we use 63 percent of our household culinary water supply in the landscape.
If each resident in this study reduced their water use again this year by just 15 percent, it would save 70,210,140 gallons of water (215 acre-feet).
Culinary Water Waste at Large Water Use Sites
The Parks, schools and public facilities evaluated in this study were generally more wasteful than homeowners. The initial group of properties studied during 1995 and 1996 used an average of 79.1 inches of water (319 percent of the turf standard water use of 24.7 inches). Adding all of the apartments, churches, parks, schools and public facilities now in the data base, the average water use is down to 276 percent (68.2 inches) of the standard which is still a horrendous amount of water to waste. This is far greater than the 201 percent of standard use by the average homeowner.
The total wasted annually by 69 parks, schools and public facilities during 1996 was 2,217 acre-feet. This is enough water to supply 5,695 average residential landscapes for an entire growing season.
Water Savings
For the large water users who received an irrigation system water audit during 1996, they were able to reduce their outdoor water use by 19.1 percent. This amounted to 690,404 gallons per property. All together they saved 146 acre-feet or 47,435.168 gallons of culinary water. The second year after the water audit, they reduced their 1998 water use by 38.7 percent compared to the 1996 records. The average water saved per park and school site could irrigate an average residential landscape for 25 years.
Most of these water savings were accomplished by a sprinkler system tune-up, purchasing more modern controllers, and paying attention to irrigation scheduling. When an entire sprinkler system is replaced with an automated system based on a weather station, the total water used can be brought down to the same level as the standard. Majestic Elementary School reduced their water use from 187 percent of the standard to 106 percent the year following automation.
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Current Cost of Water
Back in 1996, the Utah Division of Water Resources indicated that the average cost of water nationally was $1.96 and in the western United States the average cost was $1.63. While in Utah, the average cost was $1.16 per 1000 gallons of culinary water. Today, the cost of water has increased to $1.79 per 1000 gallons of culinary water. That is a 54 percent increase over a six-year period.
(a) The pricing of water is complex in many cities. The cost of total water used indoors was the base price plus 7,480 gallons plus the cost of 40,000 gallons of water used outdoors. Jim Lewis of Salt Lake City Public Utilities is thanked for his assistance.
Utah State University, Utah Counties and the U.S. Department of Agriculture Cooperating
Utah State Extension does not discriminate on the basis of race, color, national origin, gender, religion, age, disability, political believes, or martital or family status in employment or program delivery
Questions or further information regarding this paper should be directed to:
Earl Jackson, Salt Lake County Agent
2001 South State Street, Room S1200
Salt Lake City, Utah 84190-2350
Phone:(801) 468-3170