How to Determine Your Well Flow Rate

The flow rate from your well pump must be measured accurately to insure that the filter will backwash and clean the media properly. Don't make a bad purchase choice by not doing your homework! Know the system backwash rate (shown on each product link) before buying any filter!

The well water flow rate is determined by (a) timing the pump cycle and (b) counting the gallons drawn. First, make the pump come on by running a faucet. Then making sure that there are no fixtures running during the test, time the entire pump cycle from the cut in (pump on) to the end of the pump cycle cut out (pump off). Then with the pump off, open a spigot at the pressure tank or at a nearby fixture capturing the water in a bucket until the well pump turns on. Measure the amount of water you took out.

The formula for determining well flow rate is: (Gallons drawn) divided by the (number of seconds timed for the pump cycle), then multiplied by 60 equals the gallons per minute (GPM) that your pump produces.

Example One: If 8 gallons are drawn and it takes 45 seconds to build pressure back up, then: 8 divided by 45 = 0.178. Then multiply 0.177 x 60 = 10.7 gallons per minute well pump flow rate.

Example Two: If 5.5 gallons are drawn and it takes 38 seconds to build pressure back up, then: 5.5 divided by 38 = 0.145. The multiply 0.145 x 60 = 8.7 gallons per minute well pump flow rate.

Note: Do not flow water from any spigot or outside faucet and try to determine the well flow rate this way.