Cumulative risk analysis of contaminant occurrence in United States drinking water for the period of 2010–2017 indicates that over 100,000 lifetime cancer cases could be due to carcinogenic chemicals in tap water. The majority of this risk is due to the presence of arsenic, disinfection byproducts and radioactive contaminants. For different states within the U.S., cumulative cancer risk for drinking water contaminants ranges between 1 × 10−4 and 1 × 10−3, similar to the range of cumulative cancer risks reported for air pollutants. Overall, national attributable risk due to tap water contaminants is approximately 4 × 10−4, which is two orders of magnitude higher than the de minimus cancer risk of one-in-a-million. Thus, decreasing the levels of chemical contaminants in drinking water represents an important opportunity for protecting public health.