How to use this calculator
Find the flow rate stamped on the showerhead or faucet aerator (in gallons per minute, gpm), or measure it: time how long it takes to fill a 1-gallon bucket and divide 60 by the seconds. Enter the minutes per use and how many uses there are per day; the number of days defaults to a year. Add your combined water and sewer rate from your utility bill to see the cost.
Many bills charge per CCF (100 cubic feet, 748 gallons) — choose that unit for the price. Run the calculator backwards to set a budget: enter a target number of gallons per day and the flow rate to get the shower length that fits.
The formula
- q
- flow rate of the fixture
- t
- minutes per use
- u
- uses per day
- V_day
- water per day
- d
- number of days
- V
- total water used
- p
- water + sewer price
- C
- cost
Worked example
Two people each take an 8-minute shower a day under a 2.0 gpm WaterSense showerhead. Water and sewer together cost $5 per 1,000 gallons.
- Per day: 2.0 gpm × 8 min × 2 showers = 32 gallons.
- Per year: 32 × 365 = 11,680 gallons.
- Cost: 11,680 × $5 ÷ 1,000 = $58.40 a year, before heating the water.
With the federal-maximum 2.5 gpm head instead, the same showers would use 14,600 gallons a year.
Typical fixture flow rates
| Fixture | Flow |
|---|---|
| Showerhead, US federal maximum | 2.5 gpm (9.5 L/min) |
| Showerhead, WaterSense labeled | 2.0 gpm or less (7.6 L/min) |
| Bathroom faucet, WaterSense | 1.5 gpm or less |
| Kitchen faucet, US maximum | 2.2 gpm |
| Garden hose, ⅝ in | about 9–17 gpm |
Maximums are from the US Energy Policy Act and EPA WaterSense specifications.
Assumptions and limits
- Constant flow while the fixture runs. Older showerheads can exceed their rating; low water pressure reduces flow.
- Cost covers water and sewer only. Heating shower water usually costs more than the water itself — see the electricity cost calculator.
Frequently asked questions
How much water does a 10-minute shower use?
About 25 gallons with a 2.5 gpm showerhead, or 20 gallons with a 2.0 gpm WaterSense model.
How much water does an average American use per day?
The EPA estimates an average family uses more than 300 gallons per day at home, about 70% of it indoors.
What is a CCF on my water bill?
One hundred cubic feet of water, equal to 748 US gallons.