When did the maximum rate of water usage begin to be mandated?

A low-flow fixture is a water saving plumbing fixture designed to achieve water savings by having a lower flow rate of water or a smaller quantity per flush. Some of these low-flow fixtures are faucets, showerheads, and toilets. In the United States a maximum water usage of conventional plumbing fixtures was federally mandated by the Energy policy act of 1992. Low-flow fixtures are designed to save water over conventional fixtures by having a lower flow rate while still maintaining satisfactory performance. The Environmental protection agency (EPA) WaterSense program has requirements for plumbing fixtures to achieve their definition for water saving low-flow.

1992