How Many Liters of Water Is Used to Flush a Toilet?

Ultra-low-flow toilet (ULFT) bowl systems use an average of 1.6 gallons of water to properly flush the contents of a toilet bowl, while high efficiency toilet (HET) models use an average of 1.3 gallons to completely flush toilet bowl contents. Older toilet bowl system models such as those made in the 1980s to the 1990s use around 3.5 gallons of water per toilet bowl flushing. A United States Federal Law enacted in 1992 and that became a law in 1994 mandates that all toilet bowl systems manufactured in the U.S. should only use 6 liters of water or less.

In the United States, toilet bowl flushing takes up about 31 percent of a household's entire water consumption. Each person in the household flushes the toilet five times daily on average. A household with a family of four using an ULFT system will use about 26,000 gallons of water each year for toilet flushing alone.

Toilet system efficiency is rated with the WaterSense label. WaterSense is an independent water efficiency testing group comparable to EnergyStar. Toilet systems that earn the WaterSense label means that the toilet system passed the efficiency criteria set by the group. Among this criteria is the standard that the toilet system must use only 1.28 gallons per flush or less.