The drip irrigation systems in current use were developed in arid Israel in the 1960s, and water conservation remains one of the primary motivations for installing one in your garden. The components of a typical system consist primarily of polybutylene tubing, a filter, a pressure regulator and various types of emitters to release the water. The number of emitters and their sizes determine how much water the system uses.
Types of Drip Emitters
The classic drip emitter is a plastic disk with an outlet on one side and a barbed connector on the other for connecting to the water line. The flow rate of an emitter, measured in gallons per hour, is denoted by its color, and the rates vary from one-half to 4 GPH. Most emitters are pressure compensating, meaning that their flow rate is independent of the supply pressure. Besides drippers, you can also install bubblers, which supply water to a small areas above-ground, or mini-sprinklers, which have wider ranges than bubblers.
Total System Usage
If your system consists of only emitters, calculating the amount of water it uses isn't complicated. You simply count the emitters with a particular flow rate and multiply that number by the rate. Repeating this calculation for all the emitters of all rates and summing the total provides the answer. For example, if the system has 50 emitters with a rate of one-half GPH, 20 with a rate of 1 GPH and 30 with a rate of 2 GPH, the system uses (50 X 1/2 + 20 x1 + 30 x 2) = 105 gallons per hour.
Measuring Water Usage
Bubblers and mini-sprinklers are often adjustable, making it necessary to manually measure how much water each emits in order to calculate system water consumption. One way to do this is to put the sprinkler you want to measure in a 5-gallon bucket, cover the bucket and note how much time it takes the bucket to fill halfway. You then divide the amount of water in the bucket, in gallons, by the time elapsed, in hours or fractions of an hour. You can make the same measurement with drip emitters, but because water flows more slowly, it's best to fill a smaller volume, such as a tablespoon, which equals one-half ounce, or .004 gallons.
Sizing a Drip System
When you're designing a drip system, it's important to avoid including more drip components than the water system can handle. You need to measure the flow rate at the supply faucet by turning on the faucet all the way and measuring the amount of time it takes to fill a 5-gallon bucket. The time elapsed is usually a matter of seconds, so after dividing that number into the volume of water -- 5 gallons -- you multiply by 3600 to get gallons per hour. You should design your system to draw a maximum of 75 percent of that amount to allow for other draws on the supply while the drip system is on.