About the Water Usage Calculator
This water usage calculator adds up how much water your household uses from showers, baths, toilet flushes, laundry, the dishwasher, faucets, leaks and lawn irrigation. It shows gallons per day, per person, per month and per year, what that costs on your water and sewer bill, and which uses dominate.
Use it to check whether a high water bill makes sense, to see where a low-flow shower head or new toilet would save the most, or to plan for drought restrictions. Changing one input — shower minutes, toilet gallons per flush or lawn watering — instantly shows the effect on your annual bill.
Defaults reflect common fixtures: a 2.0 gallon-per-minute shower head, 1.28 gallon-per-flush toilet, about 20 gallons per load for a front-loading washer and 4 gallons per dishwasher cycle. Replace them with the ratings of your own fixtures for a closer estimate, and use the price per 1,000 gallons from your bill including sewer charges.
With the default inputs, the household water use per day is 159 gal. Change any value above to recalculate instantly.
How to use the water usage calculator
- 1Enter the number of people and typical shower habits.
- 2Check your fixtures’ ratings (shower gpm, toilet gpf) and enter them.
- 3Add weekly laundry, dishwasher loads and baths.
- 4Enter lawn or garden area and how many inches of water it gets per week.
- 5Enter your water and sewer price per 1,000 gallons to see the cost and biggest savings.
Formula and method
Each activity is converted to gallons per day: showers are people × showers × minutes × flow rate, toilets are people × flushes × gallons per flush, and faucets are people × minutes × flow rate. Weekly activities such as baths, laundry and dishwasher loads are multiplied by their water per use and divided by 7.
Outdoor watering uses the fact that one inch of water over one square foot is 0.623 gallons, so a lawn watered 1 inch a week needs area × 0.623 ÷ 7 gallons per day on average. Monthly figures are daily × 365 ÷ 12, and cost is yearly gallons ÷ 1,000 × your combined water and sewer price.
- gpm
- Gallons per minute of the shower head or faucet
- gpf
- Gallons per toilet flush
- 0.623
- Gallons per square foot per inch of water
Worked examples
Family of three with a small lawn
Showers use 3 × 8 min × 2.0 gpm = 48 gal a day, toilets 19.2, faucets 22.5, laundry 17.1, baths 5.1 and the dishwasher 2.9 — about 115 gallons indoors. Watering 500 sq ft with 1 inch a week adds 44.5 gal/day, for 159 gallons a day or about $698 a year at $12 per 1,000 gallons.
Single person in an apartment
One 6-minute shower at 2.0 gpm uses 12 gallons, five flushes 6.4 gallons, faucets 7.5 gallons and two laundry loads a week about 5.7 gallons a day — 31.6 gallons in total, or roughly 962 gallons and $11.54 a month.
Family of four with 1.6 gpf toilets and a big lawn
Indoor use is about 160 gallons a day, but watering a 2,000 sq ft lawn 1 inch a week adds 178 gallons a day — more than everything indoors. The household uses about 338 gallons a day, costing roughly $1,482 a year.
Frequently asked questions
How much water does the average person use per day?+
The U.S. EPA estimates the average American uses about 82 gallons of water a day at home, with the average family using more than 300 gallons a day. Roughly 70% is used indoors, although outdoor watering dominates in dry, hot regions.
What uses the most water in a house?+
Indoors, toilets are traditionally the biggest single use, followed by showers, faucets and clothes washers. Outdoors, lawn and garden irrigation can exceed all indoor use combined during summer.
How many gallons does a shower use?+
Multiply minutes by the shower head’s flow rate. An 8-minute shower with a 2.0 gpm head uses 16 gallons; with an older 2.5 gpm head it uses 20 gallons, and with a 1.5 gpm head only 12.
How can I tell if I have a leak?+
Turn off all water, read your meter, and check it again after one or two hours with no water used. If the reading changes, you have a leak. A few drops of food colouring in a toilet tank that appear in the bowl without flushing reveal a leaking flapper.
How much does it cost to water a lawn?+
One inch of water on 1,000 sq ft is about 623 gallons. Watering that much every week for a 26-week season uses roughly 16,200 gallons, which at $12 per 1,000 gallons costs about $194.