Low-flush toilet

A low-flush toilet (or low-flow toilet or high-efficiency toilet) is a flush toilet that uses significantly less water than a full-flush toilet. Low-flush toilets use 4.8 litres (1.3 US gal; 1.1 imp gal) or less per flush, as opposed to 6 litres (1.6 US gal; 1.3 imp gal) or more. They came into use in the United States in the 1990s, in response to water conservation concerns. Low-flush toilets include single-flush models and dual-flush toilets, which typically use 1.6 USgpf for the full flush and 1.28 US for a reduced flush.

The US Environmental Protection Agency's WaterSense program provides certification that toilets meet the goal of using less than 1.6 US 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 US$90 per year, and $2,000 over the lifetime of the toilets.Dry toilets can lead to even more water savings in private homes as they use no water for flushing.

The early low-flush toilets in the U.S. often had a poor design that 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.

In 2011, the San Francisco Chronicle reported that, while low-flush toilets are estimated to have saved the city of San Francisco 20 million gallons of water per year, the reduction in water volume caused waste sludge to back up in the city sewer pipes, designed expecting a higher ratio of water to solids. The city was attempting to solve this by adding chlorine bleach to the pipes, a proposal that raised environmental objections. 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.

In 1988 Massachusetts became the first state in the U.S. to mandate the use of low-flush 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.

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