By Kelly A. Reynolds, MSPH, PhD

In December 2020, US EPA announced the availability of $1.7 million (USD) in grant funding to provide technical assistance and training to support private drinking-water well owners. According to US EPA Administrator, Andrew Wheeler: “One of EPA’s top priorities is ensuring Americans have safe drinking water, regardless of their zip code.” This investment, in predominantly rural regions, provides support in an area that is technically outside the jurisdiction of the US EPA and the Safe Drinking Water Act (SDWA) that guides municipal water suppliers. Thus, private well owners are responsible for the construction, use, maintenance and testing of their supply. This can be a daunting task given the multitude of hazards that could compromise groundwater quality over time. New support for education and training in private well construction and water treatment, along with new technologies for quality monitoring, promises to improve the safety of well water supplies.

Priority contaminant management
According to US EPA, a private well is defined as a well owned by a homeowner, or group of homeowners, that supplies potable water to less than 25 people via fewer than 15 service connections. Over 13 million households and an estimated 30 million people in America obtain their water from private wells.1 These groundwater supplies are subject to both microbial and chemical hazards that lead to adverse human health effects. From 1971 to 2010, the US Centers for Disease Control and Prevention (CDC) found that microbes, including hepatitis A virus, Giardia, Campylobacter, E. coli, Shigella, Cryptosporidium and Salmonella were the top causes of outbreaks from wells. Waterborne microbial contaminants are usually spread via ingestion and can cause acute health effects, like stomach flu and diarrhea or more chronic conditions including liver and heart disease, diabetes and arthritis.

The most common chemical causes of well water outbreaks during this same time included arsenic, gasoline, nitrates, phenol and selenium.2 Routine testing of well water for lead and radioactive contaminants is also recommended. Local test labs can provide a complete list of bacteria, minerals, metals and organic compounds further recommended for your area. Chemical contaminants may cause acute effects such as skin rashes and impaired motor skills or chronic conditions including neurological disorders, developmental disabilities and cancer. Consumers may be exposed to waterborne chemical contaminants via ingestion, inhalation and dermal routes. Exposure to arsenic, a naturally occurring contaminant in soils, rocks and (incidentally) groundwater, can lead to lung, bladder and skin cancers. Arsenic-related cancers are estimated to result in a disease burden cost of $1.6 billion in the US every year.

Well water vulnerability
Most microbial and chemical contaminants are undetectable by taste, sight or smell. A common means of evaluating microbial well water quality includes routine monitoring for coliform or fecal coliform bacteria. Large-scale well water studies have commonly found indicators of fecal contamination in private supplies. A 2018 study in Maryland sampled 118 private wells and found that over 43 percent did not meet federal health-based regulatory standards and over 15 percent tested positive for fecal bacteria.3 Similar studies in Pennsylvania, Virginia and Wisconsin have also shown that municipal health-based standards for water supplies were exceeded nearly half the time in private well water supplies.

Microbes are the primary cause of private well outbreaks and are associated with some of the highest cost burdens relative to waterborne disease.4 Microbial indicators, however, do not provide a complete picture of overall water quality and testing for the wide array of possible microbial contaminants can be expensive and time-consuming. Furthermore, testing for fecal indicator bacteria, or specifically E. coli, does not provide information on where the contamination comes from since they are present in the feces of animals and humans. Having a means to track contaminants back to their source would be useful for improved management.

Site-specific tracking tools
For information on wells in your region, including state regulatory requirements, water quality information and testing services, US EPA provides resources organized by links to geographical regions and specific states at Different states have varying levels of resources available to help homeowners, including emergency hot lines and extension services. Consumers, however, must navigate these resources on their own and some sites are neither well developed nor user-friendly.

New tools in water quality monitoring have been developed that can assess contamination from the most common sources: agriculture and domestic wastewater systems. Recently, a group of researchers from Ireland published a scientific paper on fingerprinting techniques that use common wastewater chemical profiles to distinguish private well water contamination sources.5 Different chemical profiles are common to human versus animal wastewater sources. For example, ionic ratios (e.g. potassium/sodium or chloride/bromide), artificial sweeteners, caffeine, fluorescent whitening compounds, fecal sterol profiles and pharmaceuticals occur in different proportions in human and animal wastewater and show promise for source tracking. The fingerprinting method was validated on 212 private well samples testing, 15 percent of which tested positive for E. coli and 54 percent of a sub-sample of 24 samples were contaminated with E. coli at some point over 14 months of extensive monitoring. Low-cost fingerprinting techniques evaluating chloride/bromide and potassium/sodium ratios were useful differentiating tools of wastewater contaminant sources in well water supplies.5

Final thoughts
In the US and much of the world, private well water supplies are unregulated, untested and untreated, and consumer awareness of primary protective actions such as water treatment, source maintenance and routine testing is often low.6 Expanding educational resources and service access may improve such stewardship activities but compliance will still fall short of routine testing requirements for municipalities. Changes in environmental and equipment conditions can result in unexpected contamination events. For many private well owners, a POU treatment system provides an efficient and essential safeguard against exposure to hazards in well water supplies, especially when testing and treatment are non-existent or intermittent.


  1. Paul Haring J., Hernandez L., Trainor B. et al. American Housing Survey for the United States: 2007. Washington, DC, 2008.
  2. CDC, Water Related Diseases and Contaminants in Private Wells. 7 April 2014. [Online]. Available: [Accessed 11 January 2021].
  3. Muray, R.T., R.E. Rosenberg Goldstein, E.F. Maring, et al. “Prevalence of Microbiological and Chemical Contaminants in Private Drinking Water Wells in Maryland, USA.” International Journal of Environmental Research and Public Health, vol. 15, no. 8, pp. 1686-1698, 2018.
  4. Verhougstraete, M.P., K.A. Reynolds, J. Pearce-Walker, C. Gerba. “Cost-benefit Analysis of Point-of-Use Devices for Health Risks Reduction from Pathogens in Drinking Water.” Journal of Water and Health, vol. 18, no. 6, pp. 968-982, 2020.
  5. Fennell, C, B Misstear, D O’Connell, et al. “An assessment of contamination fingerprinting techniques for determining the impact of domestic wastewater treatment systems on private well supplies.” Environmental Pollution, vol. 268, p. 115687, 2021.
  6. Hynds, P, B. Misstear, L. Gill, “Unregulated private wells in the Republic of Ireland: Consumer awareness, source susceptibility and protective actions.” Journal of Environmental Management, vol. 127, pp. 278-288, 2013.

About the author
Dr. Kelly A. Reynolds is a University of Arizona Professor at the College of Public Health; Chair of Community, Environment and Policy; Program Director of Environmental Health Sciences and Director of Environment, Exposure Science and Risk Assessment Center (ESRAC). She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at [email protected]


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