Three researchers from the Energy and Environmental Policy Center at Harvard University have come up with a new method of calculating the risk from contaminants in drinking water, one that they believe takes into account some of the uncertainties in pronouncing water safe or dangerous to drink. The new method concentrates on the risk of cancer, which authors Edmund Crouch, Richard Wilson, and Lauren Zeise believe has not been properly considered in establishing drinking water standards.

Writing in the December 1983 issue of Water Resources Research, the authors state that “current [drinking water] standards for a given chemical or class of chemicals do not account for the presence of other pollutants” that could combine to create dangerous substances. According to Wilson, “Over a hundred industrial pollutants and chlorination byproducts have been found in various samples of drinking water, some of which are known carcinogens, others suspected carcinogens.” The same chlorine that solves one major health problem—the threat of bacterial disease—can thus contribute to another, according to the authors, by increasing the long-term risk of cancer. The largest risks are due to halomethanes such as chloroform and bromoform, produced as chlorine reacts with organic matter in drinking water.