How Much Water Your Toilet Uses

EPA states that the Energy Policy Act of 1992 set the maximum flush volume for gravity tank-type, flushometer tank and electromechanical hydraulic toilets at 1.6 gallons per flush. Models built before that standard, EPA says, range from 3.5 gpf to more than 5.0 gpf depending on age and model, and its own guidance elsewhere puts older toilets at as much as 6 gallons a flush.

Nothing about the appearance of a toilet tells you which side of that line it falls on. The date stamped inside the tank lid usually does.

Source: US EPA WaterSense, tank-type toilet supporting statement; US EPA WaterSense, Residential Toilets.

EPA puts toilets at nearly 30 percent of an average home’s indoor water consumption — more than showers, more than laundry, more than anything else inside the building.

That share is why a single old fixture, or a single leaking one, shows up on a bill in a way that a dripping tap does not.

Source: US EPA WaterSense, Residential Toilets.

The federal maximum is still 1.6 gallons. EPA’s WaterSense label goes further, at 1.28 gallons per flush or less — 20 percent below the standard — and unlike the first generation of low-volume fixtures, labeled models are tested for whether they actually clear the bowl.

That test is the difference between a modern low-volume toilet and the early ones that gave the idea its reputation.

According to EPA, replacing old toilets with WaterSense models cuts toilet water use by 20 to 60 percent, which it puts at nearly 13,000 gallons a year for a household, and reports savings of more than $170 per year in water costs and $3,400 over the lifetime of the toilets.

Those are EPA’s figures for a whole house, not a quote and not a promise about yours. What they are useful for is the shape of the decision: on a fixture that is old and faulty, the running cost is part of the arithmetic and usually gets left out of it.

Lift the tank lid and look at the underside and the back wall of the tank. Most fixtures carry a molded date, and many built to the standard state the flush volume on the bowl behind the seat hinge. A date before the early nineties means a pre-standard fixture unless somebody has replaced it since.

That last clause is the whole difficulty with dating a toilet from the age of the house, and it is why the town pages on this site say what the housing stock makes likely rather than what is in your bathroom.