Drip Irrigation Design Guide-Determining Your Water Source Flow Rate & Pressure
Designing & Planning Your System
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Determining Your Water Source Flow Rate & Pressure
The flow rate of your water supply determines how much water you have available for your drip emitters and micro 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 install on a single watering zone and the more zones you can run from a single irrigation valve.
Water pressure is the force pushing the flow of water through your system and is measured in pound per square inch (psi). If your water pressure is too low, drip emitters and sprayers won’t work properly. Too high a pressure and drip tubing and fittings can blow apart. A standard drip systems optimal operating pressure is between 20 to 30 psi. The higher the pressure, the greater the need for a pressure regulator in your drip system.
To determine the flow rate out of your faucet, follow these five steps:
1. Turn off any running water sources in the house (Washer, Dishwasher….ect)
2. Place a 5-gallon bucket under the faucet.
3. Quickly turn on the faucet so that it is fully open.
4. Record how many seconds it takes to fill the 5-gallon bucket (gallons per second).
5. 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.
QUICK TIP: The maximum recommended flow rate for 1/2" drip poly tubing is 240 GPH (4 GPM).
Although your water source may flow more the 240 GPH, it’s important to understand that the size of the drip tubing will limit how much water can pass through.
QUICK TIP: The maximum recommended flow rate for 3/4" drip poly tubing is 540 GPH (9 GPM).
To determine the water pressure at your faucet, follow these four steps:
1. Purchase an inexpensive water pressure gauge at your local hardware store (Around $10).
2. Screw the pressure gauge onto your hose bibb.
3. Turn on the hose bibb and read the psi (pounds per square inch) off the gauge.
4. Test the pressure at each water source you will connect too.
Drip systems operate best between 20-30 psi. Most household water systems operate at 50-70 psi. Install a pressure regulator to reduce the pressure if you measure above 40 psi.
QUICK TIP: If your household water pressure is at 90 psi or greater, it may compromise the operation of your drip regulator.
If this is the case, we recommend hiring a plumber to reduce the pressure of your household water system.