Drinking California tap water over the course of a lifetime could increase the risk of cancer, according to a study published on Tuesday. Researchers with the Environmental Working Group, an advocacy non-profit, studied the combined health impacts of contaminants found in 2,737 community water systems throughout California and calculated that prolonged consumption of the contaminated water could cause almost 15,500 new cases of cancer. The study found traces of arsenic, hexavalent chromium, and disinfection byproducts in the water systems. All of these contaminants are regulated federally and on a state level. Trace amounts of some arelegally allowed in the water.