Another issue of concern is lead in drinking water. Typically, lead gets into drinking water after the water leaves the treatment plant. The source of lead is most likely pipe or solder in older service connections or older plumbing inside homes, from which lead “leaks” into the water through corrosion. EPA’s lead and copper rule set an “action level” of 15 parts per billion (ppb), which is different from a maximum contaminant level.
If tests show that the level of lead drinking water is in the area of 15 ppb or higher, it is advisable – especially if there are young children in the home – to replace old pipes, to filter water or to use bottled water. EPA estimates that more than 40 million U.S. residents use water “that can contain lead in excess of 15 ppb”. In Washington, DC these concerns have led to a $408 million program carried out since 2004 to replace lead service connections to about 35,000 homes. The effectiveness of the program has, however, been put in question in 2008 by WASA, the city’s utility.
Source and References http://en.wikipedia.org/wiki/Drinking_water_quality_in_the_United_States