Inorganic and Organic Chemical Mixtures Detected in both Public and Private Tap Water in Cape Cod, Massachusetts Active

The role of contaminant exposure through drinking-water in human-health outcomes remains limited, in part, because measurements are not commonly conducted at the point of consumption—at the tap. In the United States, Federal and State agencies regulate and monitor publicly supplied drinking water, whereas Federal agencies are not authorized to regulate or monitor privately supplied drinking water. The result is a lack of directly comparable information between private and public tap water supplies.

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To address this lack of information, U.S. Geological Survey (USGS) scientists and partners in academia, the U.S. Environmental Protection Agency, and National Institutes of Health compared privately and publicly supplied residential point-of-use tap water at Cape Cod, Massachusetts, where both supplies share the same groundwater source. The Cape Cod aquifer is a single continuous unconfined aquifer that currently serves as the sole source of drinking water for more than 140,000 permanent and 400,000 seasonal residents of Cape Cod, Massachusetts.

Tap water samples collected from 10 privately supplied and 10 publicly supplied residences were analyzed for 487 organic, 38 inorganic, 8 microbial indicators, and the bioactivities of 3 hormones. Concentrations were put into context with existing Federal, State, and local health benchmark values. Scientists also utilized a and screening-level assessment to estimate biological activity of the regulated and unregulated chemicals or elements in each tap-water sample.

Multiple detections of regulated and unregulated (inorganic, organic) chemicals were detected in both privately and publicly supplied tap water. Seventy organic (for example, disinfection byproducts, pesticides, and per- and polyfluoroalkyl substances (PFAS), pharmaceuticals, and volatile organic compounds) and 28 inorganic (for example, lead, arsenic, manganese, copper, nitrate, and barium) constituents were detected in tap water. The median numbers of detections were comparable, but the median cumulative concentrations were substantially higher in public supply than in the private supply samples mainly owing to the occurrence of disinfection byproducts from chemical disinfection. Conversely, concentrations of inorganic constituents, like nitrate, lead, and copper, were greater in privately supplied residential tap water.  

The extensive data generated in this study at Cape Cod along with studies in Chicago and across the United States provide information about contaminants in public and privately supplied drinking water. The results emphasize the importance of sampling at the tap where human exposure occurs and obtaining comparable public and privately supplied drinking water information to understand human exposure.  

The Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) of the USGS Ecosystems Mission Area supported this study.