How to Calculate a Home's Water GPM

A home’s water usage is expressed in gallons per minute (GPM).
Determining the current water usage in your shower helps you choose a low-flow shower fixture to conserve water.Determining the current water usage in your shower helps you choose a low-flow shower fixture to conserve water.
You may want to calculate your water usage to compare it to your water bill or to purchase a new hot water heater that can supply adequate hot water to several areas in your home at once. Bathroom water usage is about 75% of the total water use in a home. Low-flow shower heads and toilets reduce the amount of water that is allowed to move through the water lines and thus saves you money.

Step 1

Place an empty one-gallon container under the kitchen faucet. Turn the faucet on all the way and simultaneously start a stopwatch or timer.

Step 2

Stop the stopwatch as soon as the container is full. Turn the water faucet off.

Step 3

Write the amount of time in seconds that it took to fill the container on paper with a pen. Divide the 60 seconds in a minute by the number of seconds it took to fill the container. For example, if it took 20 seconds to fill the container, divide 60 by 20 to equal three gallons per minute for this faucet. Record this number on paper with a pen as the kitchen GPM.

Step 4

Repeat these steps to record the water flow rate of each faucet in the home and write each one down. Add all of the GPM’s together to get the sum of gallons per minute in your home.

Things You Will Need

  • One gallon container
  • Stopwatch or timer
  • Pen and paper
  • Calculator