The purpose of the Lead and Copper Rule is to protect public health by minimizing lead and copper levels in drinking water. Lead and copper enter drinking water mainly from corrosion of lead and copper containing plumbing materials. The rule establishes action levels for lead and copper based on a 90th percentile level of tap water samples. An action level exceedance is not a violation but triggers other requirements to minimize exposure to lead and copper in drinking water, including water quality parameter monitoring, corrosion control treatment, source water monitoring/treatment, public education, and lead service line replacement. All community water supplies and nontransient noncommunity water supplies are subject to the Lead and Copper Rule requirements.