A drip irrigation system depends on the correct amount of water flowing into the system, so you must figure the amount of water flowing through your drip irrigation system at any particular time. Calculating the correct amount of water used is also a good way to verify if regulators are working correctly. If you are using different outlets that are tied into the same system, you need to check how much water is coming through each faucet while the other faucets or water sources are on as well as off to check if the system is working as planned.
Find a clean bucket or container that holds one gallon of water with the one-gallon mark clearly marked on the container and set near, but not under, the water source being measured.
Hold a watch with a minute hand or a stop watch in one hand and prepare to turn on the water source with the other hand.
Turn on the water source at full force.
With your free hand, move the one-gallon container under the water source and record the time it takes for the water to fill the one-gallon container. Turn water source off.
Calculate GPH or gallons per hour. For example, if it takes 15 seconds to fill the one-gallon container, then the flow would be 4 gallons per minute. Since there are 60 minutes in an hour, then the number of gallons per hour flowing from the water source would be 240 gallons. Most drip irrigation supplies and descriptions use GPH as the standard measure.