Lead and copper enter drinking water primarily through plumbing materials. Exposure to lead and copper may cause health problems ranging from stomach distress to brain damage.

The "lead and copper rule" was introduced by the United States Environmental Protection Agency in 1991. This rule defines the acceptable limits (action levels) for lead and copper in drinking water.

90% of a water system's service households must be below the following limits for lead and copper

• The action level for copper is 1.3 milligrams per liter
• The action level for lead is 0.015 milligrams per liter

That is, the treatment technique for the rule requires systems to monitor drinking water at customer taps.If lead concentrations exceed an action level of 15 ppb or copper concentrations exceed an action level of 1.3 ppm in more than 10% of customer taps sampled, the system must undertake a number of additional actions to control corrosion. If the action level for lead is exceeded, the system must also inform the public about steps they should take to protect their health and may have to replace lead service lines under their control.