Calculating Your Well Water Flow Rate November 15, 2017 17:15

Knowing the flow rate that your well can deliver to your home is an important bit of information to have when choosing many different kinds of backwashing water filters or water softeners. If you are a rural dweller with your own water system, you very likely have a pump and a pressure tank which comprise the main components of your water delivery system. Most wells use submersible pumps which reside in the well itself, but there are also jet pumps which typically sit on dry land - either in the home or in the pump house.

The flow rate calculation method described below requires that you have a pressure tank. The vast majority of rural water systems will have one, but if not you won't be able to use this method. Here's what some typical pressure tanks look like:

Pressure Tank w Water Softener

Pressure Tank w Water Filter

Pressure tank for water softener installation

Here's what you'll need to perform this test:

  • stopwatch
  • 5-gallon bucket

Once you've identified where your pressure tank is, here's what you need to do:

  • make sure your pump is not running and make sure no water is flowing anywhere in your home
  • go to a faucet in your home (preferably a high flow outlet like a bathtub), and open the faucet all the way - both hot and cold - as you start the stopwatch
  • if you have help, you can open two faucets at the same time for a more accurate result
  • stand beside the pressure tank and when you hear your well pump kick on, stop the stopwatch
  • record the number of minutes/seconds it took for the pump to kick on

Next steps

  • allow the well pump to fill the pressure tank (you'll know it's full when the pump shuts off)
  • ensure that no water is running anywhere else in your home
  • go to a faucet that will allow you fill the 5-gallon bucket
  • you need to be close enough to the pressure tank that you can hear the pump turn on
  • start filling the 5-gallon bucket and record how many gallons of water you can take before the pump kicks on
  • this is the volume of water¬†that the pressure tank holds - record this value

The Calculations:

You now know the time it takes for the pump to fill the pressure tank, and you know the volume of the pressure tank, so you can calculate the flow rate as follows:

Flow Rate = (Volume / Fill Time) X 60

  • for Volume use gallons
  • for Fill Time use seconds

Here's an example:

Fill Time = 30 seconds

Volume = 4 gallons

Flow Rate = (3 / 30) X 60

= 8 gallons per minute


Important: If during the test your bucket fills completely before the pump turns on, then you'll need to re-do the test with a larger bucket or vessel. But you'll need to know the volume of the vessel you use.