Toilets (also known as water closets) include tank-type toilets that are either gravity or pressure assist and either single- or dual-flush.
In the 1980s and early 90s, multiple states adopted standards setting maximum water use levels for showerheads, faucets, toilets, and urinals. Based on these standards, Congress adopted national standards on these products in the Energy Policy Act of 1992. The standard for toilets which took effect in 1994 was 1.6 gpf (gallons per flush).
Under the law, if the American Society of Mechanical Engineers (ASME) revises these standards, DOE is obligated to review ASME's action and consider revising the federal standards. If ASME does not revise the standards within five years, states are free to set more stringent standards themselves. On December 22, 2010, because ASME had not revised the standards, DOE officially waived preemption for plumbing products. This allows states to set toilet standards provided that they are more stringent than the 1994 federal standards.
California, Colorado, Georgia, and Texas have adopted toilet efficiency standards that require products to use no more than 1.28 gpf. The 2012 ASAP/ACEEE report, The Efficiency Boom, analyzed potential toilet standards based on this 1.28 gpf level, estimating savings of 92 billion gallons of water and $4.3 billion dollars in net present value through 2035. Products meeting the 1.28 gpf level currently meet the qualifications for the EPA WaterSense program (similar to ENERGY STAR but focused on helping consumers identify water-efficient products).
According to EPA, toilets are one of the primary users of water in the home, accounting for 30% of an average home's indoor water usage. In the U.S., there are an average of 1.9 toilets per home.