Water flow rate is the amount of water that flows through a pipe or tube over a certain period of time. In the United States, the water flow rate is measured in gallons per minute (GPM). Plumbers using the metric system will measure the water flow rate in liters per second (l/s).
Types of flow rates
There are 2 main types of flow rates:
- service flow rate – the regular flow rate in your home.
- peak flow rate – When flow rate is maximized via all plumbing appliance being on maximum.
Both of these flow rates are important to know so that you can ensure your faucets, toilets, and showers are able to function properly in any situation.
How do you calculate the water flow rate?
The equation for the flow rate is as follows:
Flow rate = Velocity * Volume of Water
You can calculate your plumbing appliance’s flow rate by using the following steps:
- Set a timer for 6 seconds. Turn on the cold water up to max to ensure maximum water flow. You’ll want to catch the flowing water in a measuring cup or bucket.
- As soon as you start the timer, begin collecting the water in the bucket. Once the 6 seconds is up, stop the water.
- Use the meauring cup to determine how much water you were able to collect, and convert it into gallons (There are 16 cups in a gallon).
- Multiply the number you get by 10 and that will be the flow rate in GPM.
What affects water flow rate?
Your home’s water flow rate can be affected by a number of factors. These factors include:
- Length and diameter of the pipes
- The number of bends, rises, and falls in your pipes
- The number of valves and fittings in your pipe layout
- The conditions of the entrances and exits of the pipes (ex: clogged pipes)
What hot water flow rate do i need?
If you are looking to purchase a tankless water heater or other heating appliance, you’ll want to be able to calculate the correct GPM you’ll need for your home. Below is a rough estimate of what the hot water flow rate should be:
- 1-2 people—23 to 36 gallons
- 2-4 people—36 to 46 gallons
- 3-5 people—46 to 56 gallons
- 5 or more people—over 56 gallons (add 10 gallons per additional person)
What is the water flow rate for a shower?
A shower’s water flow rate will be about 2-2.5 GPM. Showerheads that have a WaterSense label will not be any higher than 2 GPM as they are required to meet EPA’s specifications for water efficiency.