Researchers at the University of Massachusetts Amherst are seeking ways to curb a threat to water supplies. Natural organic matter in reservoirs, can, when combined with chlorine at treatment plants, became carcinogenic in some cases. The UMass team is involved in a three year project to try to keep organic debris out of reservoirs and rivers. David Reckhow directs the Environmental Institute at UMass. He says before coming in contact with chlorine, the organic matter is harmless.