Landscape Irrigation Equipment Part 9: Water Sources

Prepared by W. Bryan Smith, Area Extension Agent. Agricultural Engineer, Clemson University. (New 5/08.)

HGIC 1818

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Municipal Water Systems

Irrigation systems utilizing municipal or county water are supplied through a water meter. Water meters range in size from ⅝ inches to 2 inches or more. For a typical landscape system a ⅝ or ¾ inch water meter should allow adequate water flow.

Figure 1. A typical water meter.
(Courtesy Dr. Tony Tyson)

In some areas with municipal water and sewer an additional “irrigation” meter may be added for the irrigation system. The client will pay for the water used through the second meter by the irrigation system, but will not be charged sewer charges since that water does not return to the sewer system. This can be an attractive option if the cost of the second meter is relatively low. If the cost of installing the irrigation meter is high the best option may be to simply use the existing meter.

Wells

Many homeowners would like to irrigate the landscape with an existing well. This is easily possible if the well has a flow rate of at least 15 gpm. There are a few points that should be considered to prevent confusion and problems.

The first point is pump size. Well drillers install a 5 gpm pump in most household wells regardless of the actual well flow rate. Your well may be rated for 15 or 20 gpm (or more), but you will have to replace the pump to obtain this flow rate for your system.

The second point concerns the pressure tank. Pressure tanks are sized based on pump flow rate. The tank is simply there to prevent constant “on/off” cycling by a pump as you use water during the day. If a larger pump is installed a larger pressure tank (or more than one) may also be required.

Well pumps are made to run continuously. Allowing a pump to operate for 20 hours will not damage the pump in any way. However, the pump is not constructed to withstand constant starts. Each time the pump starts, the “start” windings in the motor heat up due to the large amount of electrical current used. If the pump starts more than once every 5 minutes, the “start” windings will become hot and will burn out in a short time. Adding the appropriately sized pressure tank capacity will prevent this potential problem. A system designed to allow the pump to run continuously will also prevent this problem.

One final point about existing wells. Some people tend to try to estimate the capacity of the well by the amount of water in it. For instance, someone seeing water within 5 feet of the ground surface in a well may say “That’s a great well.” This water level has little if anything to do with well performance. When a well is pumped at capacity, the water level drops down to what is called the “pumping water level” or “dynamic water level.” This depth is due to the hydrogeology of the area. The standing or “static” water level is no indication of well yield.

Figure 2. Typical “drawdown” of a well while pumping.
(Figure credit: Bryan Smith)

Ponds & Rivers

Ponds and rivers also work quite well as irrigation sources. They are generally dependable water supplies and are probably the least expensive option if no well exists. There are, however, a few things to consider before planning to use a river or pond for your irrigation system.

1. If a pond has no spring or water supply it can be pumped down quickly. For instance, if a half-acre pond is used to irrigate a 1-acre lawn, the pond will drop 2 inches for every inch of water pumped onto the lawn. If we irrigate 1 inch per week for 10 weeks, we will lower the pond some 20 inches (over 1½ feet). Rainfall will help replenish the pond – just make sure the pond has adequate capacity for your plans.
2. If you plan to use drip irrigation, you will need to provide good filtration for the pond water. Algae and other organics in the pond or river may clog a screen filter relatively quickly.
3. A centrifugal pump will need to be close to the water source to operate. Pumps do not “draw” water very well, but they excel in “pushing” it. The suction line from the water body to the pump should be no more than 30 feet long, and the pump should be 15 feet in elevation or less above the water level.
4. The suction inlet screen should be at least 2 feet below the water surface to prevent “vortexing” or drawing air into the suction pipe from the water surface and thereby losing pump prime. If the water is shallower than 2 feet deep there are some options available, involving modifying a bank or using a plastic drum as a deeper well within the water body.
5. If the water source is a public river, plan on some method to secure the pump system. In some instances vandals just can’t seem to resist a pump in plain sight.
6. The pump will require electricity. If power is not available near the water source, check into the cost of providing power to the location. In some cases this can be quite expensive.
7. The pump for this system can easily be turned on and off by the irrigation timer. A pressure tank is not necessary unless there is some need for water in other areas, such as faucets. Large pumps, however, require large pressure tanks, which can add to the cost of the system.

Summary

Irrigation systems can be supplied from many different water sources.  It is very impractical to haul water for irrigation unless the area irrigated is very small see (HGIC1802, Landscape Irrigation Management Part 3: How Much Water?.) Wells and surface water bodies provide the least expensive options over time, but municipal water can easily be used if the water cost is not excessive.

Adapted from the 2007 South Carolina Master Gardener Training Manual.

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