First Flush Toilet
Pre-1994 residential and pre-1997 commercial flush toilets use 3.4 US gallons (13 L) of water per flush (gpf or lpf). In 1992, the United States Congress passed the Energy Policy Act of 1992, which mandated that beginning in 1994 common flush toilets use only 1.6 US gallons (6.1 L). In response to the Act, manufacturers produced low-flow toilets, which many consumers did not like because they often required more than one flush to remove solids. People unhappy with the reduced performance of the low-flow toilets resorted to driving across the border to Canada or Mexico, or buying salvaged toilets from older buildings. Manufacturers responded to consumers' complaints by improving the toilets. The improved products are generally identified as high efficiency toilets or HETs. HETs possess an effective flush volume of 1.3 US gallons (4.9 L) or less. HETs may be single-flush or dual-flush. A dual-flush toilet permits its user to choose between two amounts of water. Some HETs are pressure-assisted (or power-assisted or pump-assisted or vacuum-assisted).
The performance of a flush-toilet may be rated by a Maximum Performance (MaP) score. The low end of MaP scores is 250 (250 grams of simulated fecal matter). The high end of MaP scores is 1000. A toilet with a MaP score of 1000 should provide trouble-free service. It should remove all waste with a single flush; it should not plug; it should not harbor any odor; it should be easy to keep clean. The United States Environmental Protection Agency uses a MaP score of 350 as the minimum performance threshold for HETs. 1.6 gpf toilets are also sometimes referred as ULF (Ultra Low Flow) toilets.
Methods used to make up for the inadequacies of low flow toilets include using thinner toilet paper, plungers, and adding extra cups of water to the bowl manually.