The bucket test for water flow rate
How to run a bucket flow rate test properly, what a good reading looks like for common fixtures, and how to avoid the timing mistakes that skew results.
What the bucket test measures
The bucket test answers a simple question: how much water comes out of a fixture or source each minute. You fill a container of known volume, time it, and divide. Because it captures every drop that actually flows, it reflects the real output of a tap, hose bib, showerhead, well pump, or garden line, including any restriction from aerators, kinks, or partly closed valves that a spec sheet would not show.
Running the test cleanly
Open the fixture fully and let it reach a steady stream before you start, since the first surge can be uneven. Begin timing as the water enters the container and stop the instant it reaches the fill line you are measuring to. Do the test two or three times and average the seconds, because human reaction time on the stopwatch is the main source of error. A fill that lasts at least 15 to 20 seconds keeps that error small.
What a normal reading looks like
Expectations vary by fixture. Modern bathroom faucets are often rated near 1.5 gallons per minute, kitchen faucets around 1.8 to 2.2, and showerheads up to about 2.5. An outdoor hose bib might deliver 5 to 12 gallons per minute depending on supply, and a residential well pump commonly runs in a similar range. If your bucket test comes in far below the fixture's rating, a clogged aerator or a supply issue is a likely cause.
Turning flow into fill times
Once you know the flow in gallons per minute, planning tasks becomes easy. Gallons per hour is the flow times 60, so 10 gallons per minute fills a 300 gallon tank in about 30 minutes. Liters per minute, which the tool also reports, is handy for metric irrigation figures and international pump specs. Keeping all three units in front of you avoids conversion mistakes when you are sizing a system.