Irrigation Needs and Water Bill Surprises

Bryan Smith
Area Extension Agent - Irrigation / Water Quality

Irrigation contractors all seem to have one experience in common - a suburban homeowner with a new irrigation system calling to complain about a high water bill that must be due to the "broken pipe" in the yard. All too often homeowners and businesses install irrigation systems with no consideration of the amount of water used - or of the cost of the water.

Most residential and commercial landscapes will require 1 inch of water per week to remain green and beautiful. The water requirement will of course vary with plant species, stage of growth, and environmental factors, but 1 inch of water per week is a good starting point. To irrigate 1 acre with 1 inch of water requires 27,154 gallons (3,630 cubic feet) of water.

How does this compare with your normal water use? In South Carolina most residences use between 120 and 150 gallons of water per day per person. This water use includes cooking, cleaning, bathing, and sanitary purposes as well as drinking water needs. A home with four residents will use about 600 gallons of water per day on average - or about 4,200 gallons (561 cubic feet) of water per week.

Now add in an irrigation system for a 3/4 acre yard. Applying 1 inch per week would require 27,154 gallons per acre x 0.75 acres = 20,365 gallons of water per week. This is almost 5 times the "normal" weekly water use of the home! The water bill at the end of the month will be between 5 and 6 times the cost of the "normal" water bill, since the total water use for the month will have moved from 18,000 gallons (2406 cubic feet) up to 105,278 gallons (14,073 cubic feet).

Photo courtesy Hunter Industries, Inc.

Some tips to help you keep your water bill down during the summer months:

(1) Water at night. Much less water is lost to evaporation than in the daytime due to higher humidity levels and lower wind speeds. There will be no increased disease pressure provided that you do not extend the "leaf wetness period." Plant leaves will naturally become wet at night after dewfall and dry in the morning sun. Irrigating during the night works wonderfully provided that (a) the system does not begin to irrigate before dewfall and (b) the system is stopped in time for the plant leaves to dry over a "normal" period of time the next morning.

(2) Count rainfall! Unless the storm is a 2-inch-in-5-minute "gully washer" you can count almost all of the rainfall as a portion of (or total of) your irrigation needs for that week. Water that runs off does not provide any benefit to your plants, so use only a portion of the total rainfall from that "gully washer" event.

(3) Water less often and more deeply to promote deeper root growth. The worst irrigation practice for the landscape is to water daily or multiple times each day. In heavy, clay loam soils plan to water once per week with the entire week’s water needs. In sandy loam soils water twice each week with half the week’s water needs each time. Commercial vegetable producers do water daily, but they also inject fertilizer for the vegetables each day. Their focus is somewhat different also - to provide the water and fertilizer needs each day for their vegetables and produce tasty fruit rather than to promote a deep-rooted, healthy landscape plant. Deeper rooting means a hardier, more drought-tolerant plant with access to a larger volume of soil and more nutrients from that larger soil volume.

(4) Be careful when using irrigation timers. Timers are wonderful tools, but they tend to make us lazy. We depend on the timer to provide water and spend little time checking the plants and soil moisture. Inspect your lawn and landscape plantings at least once per week and check the condition of the plants and the soil. Plant water needs are dynamic - they change with time. Plan to adjust your timer to reflect these changes during the season. Turn your timer off after a nice rain for several days and allow the rain water to provide your landscape water needs for that portion of the week.

(5) Water the yard only when necessary. Bob Polomski, Horticulturalist with Clemson University, suggests that you walk across your lawn before watering. If you turn around and cannot see your footprints then it is not time to water. If your footprints are visible then it is time to begin irrigation. Watering more frequently than necessary wastes water and can leach extra water and some fertilizer down past the root zone - and out of reach of the grass and plant roots.

(6) Improve the soil in your yard. Adding soil mixtures and organic material to bedded areas will help the soil retain water longer. It will also in many cases improve the infiltration rate of water into the soil, reducing runoff. Aeration of the lawn and mulching flower beds also help lower runoff and increase water infiltration. This not only allows you to reap the full benefit from your irrigation system but also maximizes the benefit from rainfall.

(7) Check with your water utility about an "irrigation" meter. This is a second water meter for your irrigation system. There is no sewer charge for these meters since the water provided does not return to the sewer. In many locales "irrigation" meters can pay for themselves in just a year or two, while in other areas sewer charge "caps" and high installation costs or monthly fees make an irrigation meter unfeasible.

All of these tips (with the exception of the last one concerning irrigation meters) will also help homeowners with wells to conserve water. Conserving well water means a lower power bill and less impact on your well water supply - and your neighbor’s - over the dry summer months.

Clemson’s Home and Garden Information Center offers a publication titled "Irrigation Systems" (HGIC 1705). This publication provides information about irrigation equipment, times to water, frequency of irrigation, and many other useful tips. It is free and available on the web at http://hgic.clemson.edu or can be obtained from your local Extension office