A showerhead is a plumbing fixture that directs water onto a bather.
With the passage of the Energy Policy Act in 1992, Congress established showerhead standards at 2.5 gpm (gallons per minute) at 80 psi (pounds per square inch). The standards went into effect in 1994. Congress instructed DOE to update the standards when the American Society of Mechanical Engineers (ASME) amended their standards. In December 2010, with no ASME revisions on the books, DOE officially waived federal preemption of the national showerhead standard. This waiver of federal preemption allows states to set standards provided they are more stringent than the national standard.
In 2010, New York City set showerhead standards at 2.0 gpm at 80 psi, effective July 2012, followed by Colorado in June 2014 and Vermont in May 2018. 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.