A water system is found to exceed the action level if more than 10 percent of its high-risk residences contain lead levels above 15 parts per billion. In April 1994, EPA advised homeowners with submersible brass pumps installed within the last year to switch to bottled water until they could test their tap water for lead. Laboratory research done by the Natural Resources Defense Council and the Environmental Defense Fund showed that the brass parts of newer pumps release large amounts of lead during their first months of use. EPA is conducting studies to assess how the laboratory findings relate to lead concentrations in water as it comes out of the tap. Lead is rarely found in either surface water, such as lakes and rivers, or ground water, which are the sources of drinking water for many Americans.
Lead usually enters the water supply after it leaves the treatment plant.
In some systems, the water is corrosive enough to leach lead from household plumbing pipes and lead service lines through which it passes. Treatment techniques sometimes include putting additives such as lime, calcium carbonate, or phosphate and silicate-based corrosion inhibitors into the water. These additives make the water less corrosive and leave a protective coating of minerals on pipes, so that less lead can be absorbed by drinking water. Lead is especially threatening to children and infants. In large quantities it can delay physical and mental development in babies and impair mental abilities in children.