Reading your meter and your rate
Water bills use units that almost nobody encounters elsewhere. The most common US billing unit is the CCF, one hundred cubic feet, which equals 748 gallons. Some utilities bill per thousand gallons, and meters in a few systems read in cubic meters (1 cubic meter = 264.17 gallons). Convert everything to gallons first, then apply the rates. Nearly every bill has three parts: a volumetric water charge, a volumetric sewer charge usually calculated from the same metered water, and fixed monthly service charges that you pay even if you use nothing.
Worked example with the defaults: a family of four using 9,000 gallons a month at $5.00 per 1,000 gallons for water pays $45.00, plus $6.00 per 1,000 gallons for sewer, which is $54.00, plus $15.00 in fixed charges, for a $114.00 monthly bill or $1,368 a year. Divide $114.00 by 9,000 and the all-in cost is 1.267 cents per gallon, or $9.47 per CCF. Note how sewer usually costs more than the water itself, because treating wastewater is the expensive half of the system.
How much water a household really uses
The EPA puts average indoor use at about 82 gallons per person per day, and total use including outdoor watering at roughly 300 gallons a day for a family of four, which is where the 9,000-gallon default comes from. Toilets are the biggest indoor use at about 24 percent, followed by showers at 20 percent, faucets at 19 percent, clothes washers at 17 percent, and leaks at around 12 percent. That last number is worth staring at: a running toilet flapper can waste 200 gallons a day, more than $75 a month at the rates above.
Individual fixtures are easy to reason about once you know the flow rate. A standard showerhead is 2.5 gallons per minute, so an 8-minute shower is 20 gallons; a WaterSense head at 2.0 gpm makes the same shower 16 gallons. A WaterSense toilet uses 1.28 gallons per flush against 3.5 for a pre-1994 model. A modern Energy Star dishwasher uses about 4 gallons a load, far less than washing the same dishes by hand. A high-efficiency front-load washer uses roughly 15 gallons versus 40 for an older top loader.
Outdoor use and rate tiers
Lawn irrigation is what turns a modest bill into a large one. Putting half an inch of water on 1,000 square feet takes about 312 gallons; a quarter-acre lawn watered twice a week in July can add 25,000 gallons a month. Many utilities apply increasing block rates, so that extra volume is billed in a top tier at two or three times the base rate, and some add drought surcharges. Several utilities also cap your sewer charge at your average winter usage, on the theory that irrigation water never reaches the sewer. Check whether yours does before assuming summer water is billed twice.
To check for a leak, write down the meter reading, avoid using water for two hours, and read it again. Any movement means water is going somewhere. Most meters also have a small triangular or star-shaped leak indicator that spins when water flows.