Estimate your monthly water bill from household size and usage habits.
Household water divides into showers, which you control directly, and everything else — toilets, laundry, dishwashing, taps — which runs at roughly 35 gallons per person per day and barely varies. Showers are the lever: at a standard 2.1 gpm head, an eight-minute shower is about 17 gallons, so a family of four showering daily uses 67 gallons before anything else happens. The billing catch is that most utilities charge sewer on metered water volume as well, so every gallon is effectively billed twice — the sewer rate is often close to the water rate, which means a shower costs double what the water tariff alone suggests.
Home Water Bill
Daily gallons = people x showers x minutes x 2.1 gpm + people x 35; monthly = daily x 30.44; bill = monthly/1000 x (water rate + sewer rate)
About 17 gallons for eight minutes at 2.1 gpm. An older 2.5 gpm head makes that 20 gallons, and an unrestricted rain head can exceed 4 gpm — over 30 gallons per shower.
Because it is calculated from the same meter reading. Treating wastewater costs as much as supplying clean water, so utilities apply a comparable rate to the volume you consumed.