But switching to tap water could be a bad idea in some schools where the risk of lead contamination from old pipes—known to affect physical and mental development—is high, particularly in large urban areas such as Chicago, Los Angeles, and Washington, D.C.
For instance in September 2009, the Associated Press published a nationwide investigation showing that the drinking water in schools in 27 states is contaminated with lead and other toxic substances from lead-soldered pipes generally installed before 1985.
Some school don't test the water because of the high cost of replacing pipes. They find it more cost-effective to serve bottled water, or even soft drinks to children. Link
(image credit: Flickr user Isobel T)