A showerhead is a plumbing fixture that directs water onto a bather.
With the passage of the Energy Policy Act in 1992, Congress adopted standards for showerheads at 2.5 gpm (gallons per minute) at 80 psi (pounds per square inch). The standards went into effect in 1994. 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. ASME did not revise the standards within the five years. On December 22, 2010, DOE officially waived preemption for showerheads (along with faucets, toilets and urinals), allowing states to set standards provided that they are more stringent than the 1994 national standards.
In 2010, New York City set showerhead standards at 2.0 gpm at 80 psi, effective July 2012, followed by Colorado in June 2014. In California, following the Governor's 2015 emergency declaration (drought-related), the California Energy Commission (CEC) set a 2-tier showerhead standard. Tier 1, effective July 1, 2016, sets a maximum flow rate of 2.0 gpm at 80 psi. Tier 2, effective July 1, 2018, sets a maximum flow rate of 1.8 gpm. CEC also set minimim performance requirements to ensure consumer safety and satisfaction.
Showerheads meeting the 2.0 gpm maximum can earn the WaterSense label. WaterSense is an EPA partnership program (similar to EnergyStar) which identifies products that save water and energy, save money, and meet a minimum threshold of performance.
According to EPA's Water Sense, If every household in the US switched to a 2.0 gpm WaterSense labeled showerhead, "we could save more than $2.2 billion in water utility bills and more than 260 billion gallons of water annually. In addition, we could avoid about $2.6 billion in energy costs for heating water." They note that showering accounts for about 17% of indoor residential water use.