Flow rate for any water pipe is calculated in gallons per minute (GPM). Specialized tools accurately measure the flow rate by attaching to an open line and gauging how much water or liquid passes through the tool within a specified time frame. Calculating the GPM of a water well does not require the use of special tools. A 5gallon bucket with marks indicating the volume and a stopwatch can accurately calculate the GPM through the first attached faucet.
Things You'll Need
 5gallon bucket
 Stopwatch
 Calculator

Time the amount of time it takes to fill the water bucket up to the 5gallon mark with a stopwatch.

Convert the time to straight seconds if the stopwatch measured the time in minutes and seconds. Multiply the minutes by 60 and add to the seconds.

Divide the total seconds by 5. Divide the result by 60 to get the correct GPM flow rate.

Measure the GPM at every faucet along the line for the water well.

Add each GPM measurement together and divide by the total number of faucets measured to arrive at an average GPM flow rate for the system.
Tips & Warnings
 Measure the GPM at different points during the day for the same faucets. The flow rate is affected by a number of variables, including ambient temperature of the water. Measuring the flow rate at different points gives you a more accurate picture of the precise flow rate for the water well.
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References
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