Closing Water Security Gaps in the United States: The Role of Environmental Engineers and Scientists

By official U.S. statistics reported to the United Nations Sustainable Development Goals (SDG) program, 97.6% of Americans have access to safely managed drinking water. However, these estimates overlook many population segments that struggle to access safe drinking water. The United Nations defines safely managed drinking water as water that is on premises, available when needed, and free of fecal and priority chemical contamination. U.S. estimates rely on census data on piped water access and U.S. Environmental Protection Agency (EPA) data on violations of selected health-based standards in community water systems. These metrics fail to capture major dimensions of water insecurity, summarized in Table . Table suggests that 37–55 million U.S. residents could be water insecure, representing about 11–16% of the 2024 population.

1. Water Insecure U.S. Population Segments.

drinking water gap	description	U.S. population at risk (millions)	unsafe or unreliable water (%)	water insecure population (millions)
unregulated private water systems	private wells, springs, cisterns, and other sources unregulated by the Safe Drinking Water Act	45.8	35 (16–55)	16 (7.2–25)
community water systems noncompliant with safe drinking water regulations	community water systems delivering water that does not meet health-based standards	19	100	19
households whose community water service has been shut off	water shut off due to bill nonpayment	8.5	100	8.5
homes without indoor plumbing	lack of hot and cold running water, a sink, a shower/bath, or a flush toilet	1.4	100	1.4
homeless populations	individuals or families without permanent shelter	0.6	86	0.52
total				45 (37–55)

^aMurray, A.; Hall, A.; Riveros-Iregui, D. A Machine Learning Approach to Estimate Domestic Use of Public and Private Water Sources in the United States. Water Res. 2025.

^bAverage and range of estimates from the following studies: Gleason, J. A.; O’Neill, H. S.; Schwartz, R. I.; Procopio, N. A. Twenty Years of Private Well Testing in New Jersey: A Review of the United States’s Most Comprehensive Well Water Testing Regulation. Water Policy. IWA Publishing, 2024, pp 309–320. DeSimone, L. A.; Hamilton, P. A. Quality of Water from Domestic Wells in Principal Aquifers of the United States, 1991–2004. Reston, VA, 2009. Millner, S.; Malina, N.; Rogers, S. R.; Henderson, E.; Ojeda, A. S. Drinking Private Well Water: Groundwater Quality and Management of Wells in Southern Alabama. J. Water Health 2025, 23 (2), 260–275 (10.2166/wh.2025.380). Murray, R. T.; Rosenberg Goldstein, R. E.; Maring, E. F.; Pee, D. G.; Aspinwall, K.; Wilson, S. M.; Sapkota, A. R. Prevalence of Microbiological and Chemical Contaminants in Private Drinking Water Wells in Maryland, Usa. Int. J. Environ. Res. Public Health 2018, 15 (8) (10.3390/ijerph15081686). Swistock, B. R.; Clemens, S.; Sharpe, W. Drinking Water Quality in Rural Pennsylvania and the Effect of Management Practices; 2009. Pieper, K.; Krometis, L.; Benham, B.; Gallagher, D. Simultaneous Influence of Geology and System Design on Drinking Water Quality in Private Systems. J. Environ. Health 2016, 79 (2).

^cAllaire, M.; Wu, H.; Lall, U. National Trends in Drinking Water Quality Violations. Proc. Natl. Acad. Sci. U. S. A. 2018, 115 (9), 2078–2083.

^dSarango, M.; Kim, D.; Harlan, S. L. The Color of Unaffordable Household Water: Racial/Ethnic Inequalities in Bills and Shutoffs across Local Water Districts in Nine Urban Areas of the United States. Local Environ. 2025.

^eMcgraw, G.; Fox, R. Closing the Water Access Gap in the United States: A National Action Plan. 2019 (closethewatergap.org) (accessed 2026-05-03).

^fLucas, D. S.; Boudreaux, C. J. When “What Works” Does Not Work: The United States’ Mission to End Homelessness. In International Studies in Entrepreneurship Moonshots and the New Industrial Policy Questioning the Mission Economy; Henrekson, M., Sanstrom, C., Stenkula, M., Eds.; Springer, 2024; pp 145–168.

Unregulated Private Water Systems

The Safe Drinking Water Act applies to only public water systems, defined as those serving at least 25 people for at least 60 days annually. Consequently, EPA compliance data used in SDG calculations exclude an estimated 45.8 million U.S. residents who rely on unregulated private systems, including wells, springs, cisterns, and hauled water. These households receive no federal oversight or routine financial support. Households must bear the full cost of construction, operation, and maintenance. When systems fail, and resources for repair are unavailable, homes may go without running water for extended periods.

No comprehensive national data on water insecurity among the population relying on private systems are available. However, studies across the United States have found that 16–55% of these systems may have water quality that is inconsistent with health-based standards established under the U.S. Safe Drinking Water Act. Contamination risks vary geographically and with the type of system (e.g., drilled well, dug well, spring, or cistern). They can originate from agricultural runoff, septic failures, industrial releases, geogenic contaminants, corrosion of household plumbing, and other sources.

Community Water Systems with Health-Based Violations

Each year, approximately 8% of community water systems, serving roughly 19 million people, violate health-based standards. Risk is disproportionately borne by rural systems and those serving low-income and minority communities, reflecting long-standing inequities in infrastructure investment and operational capacity. This population is not adequately captured in SDG calculations of safely managed drinking water because the SDGs consider only three measures of water qualityEscherichia coli, arsenic, and fluoride concentrationsneglecting many other commonly occurring contaminants, such as nitrate, lead, and organic chemical contaminants.

Unaffordable Water Bills

Water affordability presents another major, yet poorly tracked, dimension of water insecurity. Most U.S. utilities rely on service shutoffs to enforce payment. For households unable to pay, shutoffs can last weeks or months. Although national-scale data are limited, surveys suggest that 2.9% of the population experiences shutoffs in a given year, corresponding to approximately 8.5 million people (see Table ).

Homes Lacking Functional Indoor Plumbing

An estimated 1.4 million U.S. residents lacked complete plumbing as of 2014. This figure likely understates the problem by excluding homes with nonfunctional plumbing. For example, a North Carolina study documented a suburban community relying on private wells where residents could not flush toilets or bathe due to failed wells and broken pumps.

Homeless Populations

Approximately 600 000 U.S. residents were homeless in 2022. Most lack stable access to water infrastructure, relying instead on shelters, public facilities, or unsafe environmental sources such as creeks and stormwater. Given that about 86% of those without permanent homes lack transitional housing, an estimated 520 000 unhoused people experience water insecurity annually.

Closing Persistent Gaps

The U.S. Bipartisan Infrastructure Law (BIL) of 2021 aimed to decrease water insecurity by allocating more than $50 billion in water infrastructure funding to states over a five-year period and by instructing states to prioritize disadvantaged communities when distributing the funds. The legislation empowered states to craft their own definitions of “disadvantaged community”, considering affordability and other criteria. While the BIL has enabled long-delayed investments, emerging evidence suggests it has not effectively reached some of the most water insecure populations.

For example, only 24.6% of BIL funds distributed in Alabama in 2024 were awarded to disadvantaged communities, despite these communities comprising 55.4% of Alabama census tracts. Rural utilities often lack the technical expertise, staffing, and time required to navigate complex federal funding processes. As an example, interviews with rural water utilities in southern Indiana indicated that utility staff lacked knowledge about how to apply for BIL funds. Most of these utilities had only one full-time employee handling all aspects of operations and maintenance, from repairs to billing, and were so busy keeping their systems running that they could not afford the time to submit a federal funding application. Moreover, BIL funding excludes households relying on private systems and does not address the needs of those experiencing water shutoffs or homeless populations.

A Path Forward

Closing persistent U.S. water security gaps will require more than episodic infrastructure funding. A critical first step is the development of a nationwide, high-resolution map of water insecurity that incorporates all affected populations described in Table . The map must be high-resolution (at census block scale) because larger spatial scales obscure localized inequities, particularly where unserved households are embedded within otherwise well-served regions. ,

The federal government could support this effort by restoring detailed water service questions to the U.S. Census. Through 1990, the Census included the question “Do you get water from (a) a public system such as a city water department, or private company, (5) an individual drilled well, (c) an individual dug well, or (d) some other sources such as a spring, creek, river, cistern, etc.?” This question was eliminated after 1990. The federal government also could invest in other kinds of national data sets related to water security, including accurate community water system boundaries, distribution infrastructure maps, and water shutoff records. Statistical and machine learning models could further estimate household-level probabilities of water insecurity by integrating localized measurements with demographic and geospatial data.

With improved data, environmental engineers and scientists can develop targeted, cost-effective interventions and optimization models to match intervention packages to needs. These could include low-cost water quality sensors connected to apps that could support remote monitoring, enabling rural utilities or even homes relying on private systems to share maintenance services. Other creative solutions might include technologies that enable safe household- or community-scale water reuse at low cost, which could decrease water bills and associated shutoffs. Financial and governance innovations will be equally important, particularly for extending support to households outside traditional utility frameworks and supporting low-resource communities.

Implications

For most Americans, safe drinking water is taken for granted, yet for tens of millions, it remains unreliable, unaffordable, or entirely inaccessible. Closing this gap will require sustained attention to measurement, targeted investment, and coordinated technical and policy solutions. Environmental scientists and engineers have a central role to play, not only in advancing technology but also in ensuring that its benefits reach all communities. Only then can the United States credibly claim to provide safely managed drinking water for all.

Biography

Dr. Jacqueline MacDonald Gibson is the Twisdale Family Head of the Department of Civil, Construction, and Environmental Engineering at North Carolina State University. With a foundation of 13 years in high-impact public policy roles before transitioning to academia, Dr. Gibson’s research integrates advanced engineering methods to identify innovative solutions for mitigating environmental risks and shaping evidence-based public policy. Her distinguished public policy career includes serving as Associate Director of the U.S. National Research Council’s Water Science and Technology Board and acting as a liaison to the White House Office of Science and Technology Policy during her tenure with The RAND Corporation. Her interdisciplinary research addresses critical global challenges, ranging from optimizing water infrastructure to enhance public health in the United States to developing strategic frameworks for prioritizing environmental policy initiatives in the United Arab Emirates. Dr. Gibson is the Past President of the Society for Risk Analysis. She earned a dual Ph.D. in engineering and public policy and in civil and environmental engineering from Carnegie Mellon University, an M.S. in environmental science in civil engineering from the University of Illinois at Urbana-Champaign, and a B.A. in mathematics from Bryn Mawr College.

The author declares no competing financial interest.

Published as part of Environmental Science & Technology special issue “60th Anniversary of Environmental Science and Technology”.