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Household Water Usage Calculator

Household water use is dominated by a small number of fixtures. Measure showers, toilets and laundry and you have captured most of what goes through the meter indoors, without needing to read the bill and guess.

People in the householdUsed to scale the per person shower and toilet figures.Shower minutes per person per dayOne shower per person per day. Add them up if there is more than one.Shower flow rateGallons per minute. Measure with a bucket and a stopwatch rather than trusting the rating.Toilet flushes per person per dayFive is a normal assumption for a household that is out during the day.Gallons per flushModern toilets use 1.6 or less. Anything made before the early nineties is often 3.5 or more.Laundry loads per weekFor the whole household. This gets divided by seven to reach a daily figure.Gallons per laundry loadModern front loaders use 15 to 30. Older top loaders can exceed 40.

Daily household use

97.2571

Per person per day: 32.419
Showers per day: 50.4
Toilets per day: 24
Annual household use: 35,498.84

Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.

The formula this calculator uses

Daily gallons = shower use + toilet use + laundry use

G: Total household water use in gallons per day
m: Shower minutes per person per day
f: Shower flow rate in gallons per minute

How to check the result by hand

1
Measure the shower, do not trust the rating
Time a shower and check the head's flow. The rating on the box assumes a standard pressure and a new fitting; an older head on a high pressure supply can run well above it. A bucket and a stopwatch give the real figure in under a minute.
2
Count flushes and check flush volume
Five flushes per person per day is a normal assumption. For the volume, look for a stamp inside the tank or the bowl. Anything installed before the early nineties is likely to be 3.5 gallons or more.
3
Convert laundry to a daily figure
Loads per week times gallons per load, then divide by seven. Skipping the division is the single most common mistake here, and it overstates laundry sevenfold.
4
Add the three lines
The sum is the household's daily indoor use. Divide by the number of people to get the per person figure, which is the one worth comparing against published benchmarks.
5
Check it against the bill
Convert the bill to gallons first, since many utilities charge by the hundred cubic feet or the cubic metre. If the metered figure is far higher than the estimate, look for outdoor use or a leak.

For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Household Water Usage page.