Environmental Health Program Drinking Water Science

Protection of the Nation's drinking water resources is a priority for and the responsibility of the U.S. Environmental Protection Agency (EPA) under the Safe Drinking Water Act in conjunction with State and Tribal agencies and water utilities. The majority of (approximately 282 million) Americans are served by public drinking water treatment systems that monitor treated water for approximately 100 regulated contaminants prior to distribution as part of compliance monitoring required by the Safe Drinking Water Act. In addition, the Unregulated Contaminant Monitoring Rule requires monitoring of as many as 30 other contaminants every 5 years. Public water supply treatment, followed by compliance monitoring, form a cornerstone to maintaining safe public drinking water in the United States.

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Water chemistry can change, however, from the point of distribution at a drinking water facility to the taps in homes and businesses owing to leaks, cross-connections, onsite plumbing, and back-siphonage. Moreover, very few chemicals (with the exception of disinfection byproducts, disinfectant residuals, lead, and copper) are monitored at the tap in homes or businesses and novel pathogens continue to emerge.

This lack of monitoring leaves gaps in understanding if tap water contains contaminants or pathogens that might be a hazard now or in the future, and gaps in understanding human exposure through water from residential or business taps.

In addition, as many as 60 million Americans living in rural areas supply their own drinking water from onsite wells. Unlike publicly supplied water, these wells are not federally regulated, and treatment is entirely the responsibility of the homeowner. Consequently, these rural homeowners often know very little about the quality of their drinking water.

This leaves questions related to contaminants and pathogens present in drinking water consumed at the point of exposure including the following:

• What contaminants or pathogens are present in tap waters that come from publicly or privately supplied drinking water sources?
• What factors affect the types and concentrations of contaminants and pathogens present in tap water?
• Can predictive tools help us to define, prioritize, and mitigate human exposure and health risks?

U.S. Geological Survey Provides Answers

The U.S. Geological Survey (USGS) has long filled gaps and built a foundation of research on chemical mixtures detected in surface water and groundwater resources serving as source waters for drinking water, and research on chemical mixtures detected in public drinking water supplies prior to distribution to residences and businesses. 

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The USGS studies the interconnected continuum of water from it sources in watersheds through natural and built environments to the point of use at the tap. During 2016, the USGS and collaborators conducted pilot studies at business and residential taps across the Nation. Then in a 2017 follow-up study in the Greater Chicago Area, water samples were collected from the taps of 45 Chicago-area residences. The studies revealed that chemicals not commonly monitored were present in tap water samples. Consistent with previous findings in tap waters, disinfection byproducts (DBPs), low-level concentrations of per- and polyfluoroalkyl substances (PFASs), and pesticides were frequently detected. Very few of the more than 500 chemicals measured exceeded regulatory guidelines. Although no enforceable guidelines were exceeded, drinking water goals used to manage public drinking water supplies for arsenic, lead, uranium, and two DBPs (bromodichloromethane and tribromomethane) were exceeded. The results of these initial pilot studies emphasized the high quality and effective treatment of the public drinking water in the areas sampled. The results also demonstrated the potential for human exposure to low concentrations of chemicals in mixtures that are not commonly monitored or assessed at the point of exposure. The occurrence of these chemicals does not necessarily indicate adverse effects because currently there is a gap in the understanding of whether exposure to these chemical mixtures affect human health.

Research supported by the USGS Environmental Health Program continues to foster collaborations with public health experts outside the USGS (such as National Institute of Environmental Health Sciences, Centers for Disease Control and Prevention, EPA, Public Health Departments, and academics) to help them fill these gaps by exploring linkages between contaminant exposures in tap water and health outcomes. These collaborations bring efficiency by combining USGS expertise in transport, fate, and analysis of contaminants with the public health expertise in human health outcomes.

The USGS is delivering science, data, and related information needed for decision makers who maintain the safety of U.S. drinking water supplies and for rural homeowners with private wells, those using public water supplies in urban areas, and those on tribal lands. This research helps us to understand the contaminants and pathogens in tap water and how increased reuse of wastewaters in watersheds and aquifers, aging drinking water infrastructure, legacy plumbing materials, and disinfection processes may affect contaminant exposures from drinking water. 

Read this collection of featured science articles to discover more about contaminants in drinking water and the research of the USGS Water and Wastewater Infrastructure Team in the Environmental Health Program (Toxic Substances Hydrology and Contaminant Biology) of the Ecosystems Mission Area.