Maximum Contaminant Level

For most contaminants regulated under the Safe Drinking Water Act, the EPA sets a safety goal called the Maximum Contaminant Level (MCL) – a level below which there are no known or expected health risks to people over a lifetime of exposure. Lead contaminates in a water supply may be due to lead service lines, plumbing fixtures in individual homes and private plumbing systems not Public Water Supplies (and are thus impossible to fully control at the public water system level).  Instead, EPA established a treatment technique rather than an MCL for lead. A treatment technique is an enforceable procedure or level of technological performance which water systems must follow to ensure control of a contaminant.

The treatment technique regulation for lead (referred to as the Lead and Copper Rule) requires water systems to control the corrosivity of the water. The regulation also requires systems to collect tap samples from sites served by the system that are more likely to have plumbing materials containing lead. If more than 10 percent of tap water samples exceed the lead action level of 15 parts per billion, then water systems are required to take additional actions including:

  • Taking further steps to optimize their corrosion control treatment (for water systems serving 50,000 people that have not fully optimized their corrosion control) .
  • Educating the public about lead in drinking water and actions consumers can take to reduce their exposure to lead.
  • Replacing the portions of lead service lines (lines that connect distribution mains to customers) under the water system’s control.