How To: Calculate the Output of Your Water Supply

When planning your automatic irrigation system, the first thing to work out is the output of your water supply. This is regardless of whether you have a mains water supply or water from a tank or dam. To accurately measure your water supply, you’ll need to calculate both Pressure Output & Flow Output at the connection point of your system. This will allow you to work out how many sprinklers or drippers can be run on each individual zone.

Calculating Flow

Flow is probably the most important reading to take when pre-planning your irrigation system. This can easily be done with the bucket test:

  1. Place a 9 Litre bucket under the tap you’ll be using.

  2. Open your tap full, and time how long it takes to fill.

  3. Apply the following formula to determine flow rate:

60 / (time to fill bucket in seconds) x 9

Example: A bucket takes 10 seconds to fill. 60 divided by 10 = 6

6 multiplied by the number of litres in the bucket (9) = 54 Lpm


Calculating Pressure

In a large number of areas, pressure shouldn’t be an issue & you’ll have a fair idea whether you have poor, good, or high pressure just by watching your tap when it’s open. But it is a good idea to get a pressure reading so your system works once you’ve put in all that effort to install it. To check the water pressure, attach a pressure gauge to the tap closest to the water meter. Make sure that no other water is flowing anywhere else in the house. This is the static water pressure in kPa (kilopascals).


PDF Download: HowToCalculatetheOutputofYourWaterSupply.pdf