U.S. water supplies are seriously threatened by microbes, warns a report from the American Society for Microbiology, but efforts to control water pollution have concentrated on chemical risks rather than microbial ones. The report claims that dangerous organisms such as E. coli O157, cryptosporidium, giardia, hepatitis A, and pfisteria pose a greater risk to human health than chemical pollution. Much of the microbial contamination stems from human waste that finds its way into water sources; waste from cattle and chickens is also a problem.