Determine Water Flow Rate
Four simple steps
How To Measure Flow Rate
The flow rate of your water supply determines how much water you have available for your drip emitters and sprinklers. It is commonly measured in Gallons Per Hour (GPH) or Gallons Per Minute (GPM). The greater the rate of flow of water, the more drip emitters you can put on a single watering zone and the more zones you can run from a single irrigation valve. If you are going to add a drip system to your faucet (hose bibb, spigot, hydrant), you'll need a bucket and a stop watch.
To determine the flow rate out of your faucet follow these four steps:
1. Place a 5-gallon bucket under the faucet.
2. Quickly turn on the faucet so that is fully open.
3. Record how many seconds it takes to fill the 5-gallon bucket (gallons per second).
4. Calculate your flow rate to determine Gallons per Hour:
(5 gallons ÷ X seconds) X 60 seconds/minute X 60 minutes/hour = Gallons per Hour (GPH)
Example: If it takes 75 seconds to fill our 5-gallon bucket. The formula is:
(5 gallons ÷ 75 seconds) X 60 seconds/minute X 60 minutes/hour = 240 GPH
Now you know the limit of emitter output for your system. In the example above, you can place a total of 240 1-gph or 480 1/2-gph drip emitters on your system. Note: This is only one factor in designing your system. You also need to consider water pressure and maximum run for mainline tubing. For more details, read our Drip Irrigation Basics & Installation Tutorial.
Last modified: September 21, 2011