Plumbing Fixture GPM Calculations

Gallon Test

• The most direct way to measure the flow rate of your faucet or other fixture is to see how much time it takes to fill a container that holds 1 gallon. Place the container under the tap and turn on the water. Start a stopwatch or other timer when the water starts to flow and stop once the water crests the top of the container. The final time is how long it takes 1 gallon of water to flow from the tap.

Incremental Test

• A flow-rate test that requires less space and a smaller container involves the use of a container divided into quarts. Place the container under the faucet and allow it to fill for 15 seconds. Shut off the water and see how many quarts have been filled. Multiply the number of quarts by 0.25 to convert the figure to gallons. For example, 2.2 quarts equals 0.55 gallons. Multiply the number of gallons by four to see the number of gallons per minute.

Setting Specific Aerators

• You can adjust the flow rate of most faucets by changing out the aerator inside the faucet head. Aerators slow the flow of water from the main pipe and add air into the stream for a more consistent flow. Aerators are marked on the side with the flow rate. Most kitchen sinks without an aerator, for example, will dispense up to 5 gallons per minute. Adding a low-flow aerator, you can slow that amount to about 2 gallons per minute. Experiment with a variety of aerators to help save water.

Ways to Conserve Water

• If your faucet or other fixture has a high gallon-per-minute flow rate, it's possible to adjust your habits to save water. Remember to turn off the water while brushing your teeth or washing your face until you need the water. Consider adding an electric hot water booster to your water heater to help provide hot water more quickly to the shower. Showers also use considerably less water than bathtubs. In the absence of a low-flow aerator, turning on your faucets halfway will also use less water.