Monday, November 11, 2013

How Can I Determine My Well Pump's Flow Rate?

Today's post isn't a reply to a reader letter, but a short guide intended to answer a question that we often get from well water users: "How can I determine my well pump's flow rate?"

Knowing your well pump's flow rate is crucial when purchasing or installing water treatment systems, as they come in many different sizes and will have different operating requirements based on your flow rate.
For example, say your well pump has a maximum flow rate of 5 gallons per minute. This means you can fill a 5 gallon bucket in one minute.  If you choose a backwash filter system that requires 10 gallons per minute for backwash you'll find that it won't work properly, because you need a system that functions on 5 GPM.
Luckily, determining your well flow rate is easy and only takes a few minutes:
  1. Open any faucet or hose bib (a hose bib is a faucet to which a hose can be attached; you probably have one on the side of your house or in your backyard) until your well pump turns on
  2. Close the faucet or hose bib and let your pump fill your pressure tank until the pump turns off
  3. Using your 1 or 5 gallon bucket, open the faucet again and collect and measure all water discharged until your pump turns back on
  4. When the pump turns on, immediately close the faucet and start your timer
  5. When the pump turns off again, record the time it took to refill your pressure tank in seconds
  6. Divide the number of gallons collected in Step 3 by the number of seconds recorded in Step 5
  7. Multiply the number from Step 6 by 60 – this is your pump’s average pumping capacity in gallons per minute
If you cannot tell when your pump is turning on and off, you can use your pressure switch instead.   Simply locate the pressure switch and remove its cover.  [WARNING: Live voltage is under the pressure switch cover.  Please DO NOT touch any of the live electric terminals inside.]  Note that the pressure switch has four terminals that open and close as the pump runs.  When these terminals are closed together, this means the pump is running; when they are open, the well pump is off.

To make your calculations even easier, we've provided a flow rate calculator on our website.

Please send any questions or comments to, or drop us a line on Facebook.  We love to hear from you!