In the US, lead occurs primarily as a corrosion by-product in public drinking water supplies. That is, its source is the corrosive action of the water upon the materials used in the water distribution system and private plumbing. Historically, drinking water has not been a major source of lead exposure for most Americans. However, as other sources of lead exposure continue to decline in this country, particularly decreased airborne lead from reduced use of leaded gasoline and decreased dietary lead, the relative contribution of drinking water as an exposure source has increased. This has occurred simultaneously with increasing evidence that lead's health effects occur at lower exposure levels, levels previously thought to be 'safe'. There is, however, no single, available data base for assessing exposure to lead in drinking water. In the article, the authors use a variety of data sources to develop a profile of lead levels in US public drinking water supplies, providing some upper and lower bound estimates of likely exposures as well as identifying some risk factors.