The Water Source

House wells or city water mains usually provide water for lawn and garden irrigation systems. In these instances, you need to determine the volume of water available and the pressure at which it can be supplied.

To determine the capacity of an existing well, first ensure that there is an operating pressure gauge at the well discharge or on the pressure tank. Open enough faucets so that the well pump comes on and stays on. Allow the pressure to stabilize and note the reading. The pressure should then be adjusted to match the pressure required by the sprinkler system (usually 40 to 60 psi). You can increase the pressure at the well by gradually closing One of the faucets. Decrease the pressure by opening another faucet. Once the pressure is stabilized at the desired operating pressure (this may take several minutes), measure the flow rate from each faucet in gallons per minute by using a five gallon bucket and a stopwatch. The combined flow from all of the faucets is the pumping capacity of the well at the desired operating pressure.

The volume of water available from a city water system primarily depends on the size of water meter supplying the water. The static water pressure in a city main can vary from 30 to well over 100 psi; therefore, it is a good idea to measure the pressure yourself by attaching a pressure gauge to any outside faucet. Make sure all other outlets are closed and open this faucet fully. The pressure shown on the gauge is the available static pressure in the city main. This pressure should be measured at several different times during the day to determine the minimum pressure.

Pressure loss through the meter should not be greater than 10 percent of the available static pressure. If you have 60 psi static pressure, pressure loss through the meter should be no more than 6 psi (take 10 percent of 60). In no case should flows greater than 75 percent of the maximum safe flow for the meter be used for design purposes.

The size of an existing water meter is usually cast or stamped into the meter case adjacent to the meter dial. The nominal size should also be found on the dial. Once the meter size is located, the available water supply can be determined using the preceding guidelines. The capacity of the supply tap from the water main to the meter should also be checked.

If the existing meter is not large enough, or if sewage charges are based on water usage, you may want to install a separate meter strictly for irrigation. Most municipal water systems will install a second meter for a set fee.

Given the volume of water available and the output of each individual sprinkler, divide the area into zones so all sprinklers in each zone can be operated at once. For instance, if the water capacity is 12 gallons per minute and each sprinkler has an output of 2.5 gallons per minute, a maximum of four sprinklers can be supplied in each zone.

Information provided by The University of Georgia College of Agricultural & Environmental Sciences Cooperative Extension Service.