Low-flush toilet

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A low-flow toilet is a flush toilet that uses significantly less water than a full-flush toilet. Low-flow toilets use 6 liters (1.6 gallons) or less per flush as opposed to 13.2 liters (about 3.5 gallons) as was the norm in the 1980s and prior. They came into use in the United States in the 1990s, in response to water conservation concerns.[1] Low-flow toilets include single-flush models and dual-flush toilets, which typically use 1.6 gpf for the full flush and 1.1 gpf for a reduced flush.

In 1988 Massachusetts became the first state in the country to mandate the use of low flow toilets in new construction and remodeling. In 1992, U.S. President George H. W. Bush signed the Energy Policy Act. This law made 1.6 gallons per flush a mandatory federal maximum for new toilets. This law went into effect in January 1, 1994 for residential buildings and January 1, 1997 for commercial buildings.

The first generation of low-flow toilets were designed like traditional toilets. A valve would open and the water would passively flow into the bowl. The resulting water pressure was often inadequate to carry away waste. In addition to tank-type toilets that "pull"[clarification needed] waste down, there are also now pressure-assist models, which use water pressure to effectively "push" waste.[citation needed]

The Mendelsohn House apartment complex in San Francisco replaced every 3.5 gallon traditional toilet in their 189 apartment units with 1.0 gallon high efficiency toilets equipped with Flushmate IV pressure vessels. This single apartment complex saved four million gallons of water per year.[2]

The US Environmental Protection Agency's WaterSense program provides certification that toilets meet the goal of using less than 1.6 gallons per flush. Units that meet or exceed this standard can carry the WaterSense sticker. The EPA estimates that the average US home will save $90 per year, and $2,000 over the lifetime of the toilets.[3]


Many people[who?] disliked the early low-flow toilets because they had a generally poor design that often required more than one flush to rid the bowl of solid waste; two flushes of a low-flush toilet would thus use as much water as a single, but more effective, flush of a standard toilet. In response, U.S. Congressman Joe Knollenberg from Michigan tried to get congress to repeal the law but was unsuccessful. The design and performance of low flow and ultra low flow toilets has significantly improved since 1994[citation needed].

In 2011, the San Francisco Chronicle reported that, while low-flow toilets are estimated to have saved the city of San Francisco 20 million gallons of water per year, the reduction in water volume has caused waste sludge to back up in the city sewer pipes that were designed expecting a higher ratio of water to solids. The city is attempting to solve this by adding chlorine bleach to the pipes, a proposal that has raised environmental objections.[4] In house drain system design, smaller diameter drain pipes are being used to improve flow by forcing waste to run higher in the pipe and therefore have less tendency to settle along the pipe.

See also[edit]


  1. ^ Jenkins, Matt. "A Brief History of Water Conservation in America" (web). Rate My Toilet. Retrieved November 10, 2014. 
  2. ^ "Evaluation of Water Use Reduction Achieved Through Residential Toilet Fixture Replacements". Flushmate. Retrieved 23 December 2012. 
  3. ^ "WaterSense An EPA Partnership Program". US EPA. Retrieved 23 December 2012. 
  4. ^ Ross, Andrew (February 28, 2011). "Low-flow toilets cause a stink in SF" (web). San Francisco Chronicle. Retrieved December 10, 2012.