EPA Drinking Water Violations: The Federal Database Behind Safe Drinking Water Act Enforcement

The EPA Safe Drinking Water Information System tracks every violation of the Safe Drinking Water Act by the 150,000 public water systems in the United States — health-based violations for exceeding maximum contaminant levels, monitoring failures, reporting violations, and treatment technique violations — creating the most comprehensive federal record of drinking water safety failures.

This article covers the statutory framework of the Safe Drinking Water Act and its key amendments; how the 150,000 public water systems are classified; the four principal categories of SDWA violations and how regulators distinguish health-based from procedural failures; the contaminants that drive the most serious enforcement action, including lead and copper, nitrates, coliform bacteria, arsenic, disinfection byproducts, and the new PFAS maximum contaminant levels finalized in 2024; the structural coverage gaps that leave 42 million Americans on private wells entirely outside federal oversight; the environmental justice dimension of drinking water violations; the ECHO database and how it integrates SDWIS data for public access; the enforcement mechanics from state notices of violation through EPA administrative orders and civil penalties; and how to query the EPA ECHO API programmatically to identify water systems with significant noncompliance.

SDWIS and the Safe Drinking Water Act: statutory context

Congress enacted the Safe Drinking Water Act in 1974 in response to growing evidence that tap water in American cities contained a wide range of chemical contaminants that existing state and local programs were not adequately controlling. The SDWA gave the EPA authority to establish national drinking water standards and required public water systems to comply with them. The act was substantially amended in 1986 to mandate that EPA set standards for a specific list of 83 contaminants and to establish new requirements for filtration and disinfection of surface water supplies. The 1996 amendments made a structural shift in how standards are developed: rather than requiring EPA to regulate a fixed list of contaminants on a set schedule, the amendments created a risk-based prioritization process in which EPA is required to evaluate at least 30 contaminants on a five-year cycle and to decide which, if any, warrant new maximum contaminant level regulations.

The Safe Drinking Water Information System (SDWIS), maintained by the EPA Office of Water, is the national database that tracks compliance with SDWA standards across all regulated public water systems. State primacy agencies — the state drinking water programs that hold day-to-day regulatory authority — report violation data to SDWIS through a federal reporting interface. EPA uses SDWIS to compile national compliance statistics, identify high-priority enforcement targets, respond to congressional inquiries and public records requests, and support the biennial Safe Drinking Water Act compliance reports to Congress. The public-facing version of SDWIS data is accessible through EPA's ECHO platform.

The 150,000 public water systems: classification and coverage

A public water system under the SDWA is any system that provides piped water for human consumption and serves at least 25 people or has at least 15 service connections year-round. The 150,000 regulated systems span an enormous range: from major urban utilities serving millions of people from sophisticated treatment plants with multiple barriers, to rural systems serving a few hundred residents from a single groundwater well with minimal treatment infrastructure.

EPA classifies public water systems into three categories based on the population served and the nature of service:

Community water systems (CWS) serve the same population year-round. They are the residential water utilities that supply homes, apartment buildings, and businesses in permanent communities. There are approximately 51,000 CWSs in the United States. They serve roughly 295 million Americans and are subject to the most comprehensive set of SDWA regulations. CWSs range from large metropolitan utilities — the New York City DEP system, the Los Angeles DWP, the Chicago Department of Water Management — to small rural co-ops and municipal utilities serving a few hundred households.

Non-transient non-community water systems (NTNCWS) regularly serve the same 25 or more people at least six months per year, but those people are not permanent residents. Schools, offices, factories, and hospitals that operate their own water supply fall into this category. There are approximately 17,000 NTNCWSs. Because the same individuals drink the water on a recurring basis, they are subject to long-term exposure standards for chronic health effects — the same nitrate, arsenic, and disinfection byproduct rules that apply to CWSs.

Transient non-community water systems (TNCWS) serve a transient population — different people from day to day. Rest areas, campgrounds, gas stations, and restaurants with their own water supply fall into this category. There are approximately 82,000 TNCWSs, making them the largest category by count though they serve the smallest share of total population. Because exposure is transient, TNCWSs are subject only to the standards for contaminants that pose acute health risks from single or short-term exposures — principally the microbial and nitrate standards.

The primacy system: state agencies as the front-line regulator

The SDWA created a cooperative federalism structure in which EPA sets the national standards but states administer the program on a day-to-day basis, subject to EPA oversight. A state that adopts drinking water regulations at least as stringent as EPA's federal standards, has adequate legal authority and resources to enforce those regulations, and maintains a systematic program for inspecting water systems and reviewing monitoring data can apply for primacy — the authority to be the primary regulator of public water systems within the state.

As of 2026, 49 states plus the District of Columbia have primacy. Wyomingis the one state that has not applied for primacy; EPA Region 8 directly administers the SDWA program for Wyoming's public water systems. Tribal governments may also apply for primacy for systems on tribal lands, but most tribal water systems are regulated directly by EPA. The primacy structure means that most SDWA enforcement — issuing notices of violation, requiring corrective action, and conducting inspections — is conducted by state agencies. EPA serves as the backstop: if a state fails to take timely action against a violating system, EPA has authority to step in, though it exercises that authority selectively given resource constraints.

The practical consequence of the primacy system is that the quality of SDWA enforcement varies considerably across states. States with well-funded drinking water programs, strong legal authority, and aggressive enforcement cultures — California, Massachusetts, New Jersey — typically have lower rates of unaddressed violations and faster return-to-compliance timelines than states with underfunded programs or a history of regulatory deference to water system operators. The SDWIS database reflects these differences: the national violation dataset is as much a record of state enforcement intensity as it is a pure measure of water quality failure.

Violation types: health-based versus monitoring and reporting

SDWA violations fall into four principal categories, distinguished by whether the violation reflects actual contamination exceeding health-protective limits or a procedural failure that may or may not correlate with a health risk:

Maximum Contaminant Level (MCL) violations occur when a regulated chemical or microbial contaminant in finished drinking water exceeds the legally enforceable concentration limit. MCLs are set as close to the maximum contaminant level goal (MCLG) as is feasible, where feasibility reflects available technology and the costs of treatment. MCL violations are the most directly health-relevant violation type — they indicate that people are drinking water containing a contaminant at a concentration above what EPA has determined is safe. MCL violations are counted per contaminant per monitoring period: a system that exceeds the nitrate MCL in one monitoring period and the arsenic MCL in another has two separate violations.

Maximum Residual Disinfectant Level (MRDL) violations apply to systems that use disinfectants to control microbial contamination and occur when residual disinfectant concentrations in the distribution system exceed the MRDL. Free chlorine has an MRDL of 4.0 mg/L; chloramine has an MRDL of 4.0 mg/L as Cl2; chlorine dioxide has an MRDL of 0.8 mg/L. MRDL violations are relatively uncommon because most utilities carefully manage disinfectant dosing, but they occur in systems that over-disinfect out of concern about microbial risk or that have experienced operational problems with disinfectant feed equipment.

Treatment Technique (TT) violations occur when a water system fails to follow a required treatment process rather than exceeding a concentration limit. EPA uses treatment techniques rather than MCLs for contaminants where monitoring for the contaminant itself is impractical or where the appropriate public health protection is a process requirement rather than an endpoint concentration. The most significant TT requirements are the Surface Water Treatment Rule requirements: turbidity limits on filtered water (indicating adequate filtration), disinfection contact time (CT) requirements (ensuring adequate pathogen inactivation), and watershed control and source water protection requirements. The Lead and Copper Rule is also administered as a TT rule: rather than setting an MCL for lead in finished water, it requires corrosion control treatment, lead service line replacement, and public notification when lead concentrations in tap samples exceed the action level.

Monitoring and Reporting (M&R) violations occur when a water system fails to collect the required water quality samples, fails to have samples analyzed by a certified laboratory, or fails to report monitoring results to the primacy agency on the required schedule. M&R violations do not directly establish that the water is unsafe — the system may have been in perfect compliance on the days it should have sampled — but they represent compliance gaps that prevent regulators and the public from verifying safety. Monitoring violations are the most common violation type by count in SDWIS, accounting for the majority of all violations in any given year. They are concentrated in small water systems that lack dedicated compliance staff.

A fifth category, public notification violations, occurs when a water system fails to notify its customers of an MCL exceedance, TT violation, or other significant violation within the required timeframe. For acute health risks — like an E. coli detection — notification must occur within 24 hours via radio, television, and hand delivery. For less acute violations, notification must occur within 30 days via bill inserts, newspaper, or mail. Public notification violations are particularly significant because they mean that customers were consuming potentially unsafe water without the information they needed to seek alternative sources.

Key contaminants: lead, nitrates, coliform, arsenic, PFAS

The SDWA regulates more than 90 contaminants, but a handful account for the most serious public health consequences and the most prominent enforcement actions:

Lead and copper present a distinctive regulatory challenge because the primary source of lead contamination in drinking water is not the source water or the treatment plant but the distribution system itself — lead service lines connecting the water main to household meters, lead solder in household plumbing installed before 1986, and brass fixtures containing lead alloys. The Lead and Copper Rule, first promulgated in 1991 and substantially revised in 2021, requires water systems to collect tap water samples from high-risk homes (those most likely to have lead plumbing), compute the 90th percentile lead concentration across the sample set, and compare that value to the action level of 15 parts per billion (ppb). If the 90th percentile exceeds 15 ppb, the system must take a series of required actions: corrosion control treatment, public education, water quality parameter monitoring, and — under the 2021 revision — mandatory lead service line replacement within ten years at a rate of at least 3% of known lead service lines per year.

The Flint, Michigan water crisis that emerged in 2014 and dominated national attention through 2019 stands as the most significant modern failure of the SDWA compliance system. When Flint switched its source water from the Detroit water system to the Flint River in April 2014, state and city officials failed to require corrosion control treatment despite the river water's corrosive chemistry. Without corrosion inhibitors, the river water leached lead from Flint's aging lead service line infrastructure into tap water. Lead concentrations in Flint homes exceeded 27 ppb at the 90th percentile — well above the 15 ppb action level. Blood lead levels in Flint children rose measurably. Twelve deaths were attributed to a Legionella outbreak facilitated by inadequate disinfection during the same period. Federal remediation costs exceeded $400 million; criminal charges were brought against state and city officials; litigation settlements reached into the hundreds of millions of dollars. The Flint crisis exposed systemic failures in how the Lead and Copper Rule was being implemented: the 90th percentile sampling methodology allowed systems to “game” the results by selecting sampling sites unlikely to show high lead, and state regulators had inadequate technical capacity to detect corrosion control failures in real time. The 2021 Lead and Copper Rule revision tightened sampling protocols and established a lower lead trigger level of 10 ppb, below which replacement actions begin, in addition to the 15 ppb action level.

Nitrates have a federal MCL of 10 milligrams per liter (mg/L) as nitrogen. The primary source of nitrate contamination in drinking water is agricultural runoff: nitrogen-based fertilizers applied to crop fields leach into groundwater and surface water. Septic system discharge and livestock waste are secondary sources. The principal acute health concern is methemoglobinemia — colloquially known as “blue baby syndrome” — in which nitrate reduces hemoglobin's oxygen-carrying capacity in infants under six months whose digestive systems produce bacteria that convert nitrate to nitrite. In healthy adults, nitrate at concentrations up to and modestly above 10 mg/L does not cause acute harm, though emerging epidemiological evidence links long-term elevated nitrate exposure to colorectal cancer and thyroid dysfunction. Nitrate MCL violations are concentrated in agricultural regions — the Central Valley of California, the Midwest Corn Belt, and the High Plains aquifer states — and affect both community water systems drawing from contaminated groundwater wells and individual private wells that fall entirely outside SDWA coverage.

Coliform bacteria are the primary microbial indicators in SDWA monitoring. The Total Coliform Rule requires water systems to sample for total coliform on a monthly basis, with sample counts scaled to system size. A total coliform detection in a routine sample triggers a repeat sampling requirement; if E. coli is detected in the repeat sample, or if total coliform is detected in two or more routine samples in a month, the system must notify customers immediately because of the acute risk of gastrointestinal illness. E. coli is a fecal indicator: its presence in treated drinking water indicates a failure of disinfection or a break in the distribution system integrity that allows contamination. The 2013 Revised Total Coliform Rule tightened the trigger thresholds and added requirements for systems with recurring total coliform detections to conduct sanitary surveys to identify and eliminate the source of contamination.

Arsenic occurs naturally in groundwater in many parts of the United States, particularly in the Southwest, New England, the Upper Midwest, and parts of the Mountain West, where geological formations contain arsenic-bearing minerals that dissolve into groundwater over time. The EPA set the arsenic MCL at 50 ppb from 1975 until 2006, when a revised rule lowered it to 10 ppb — the standard recommended by the World Health Organization — in response to evidence that long-term exposure at concentrations between 10 and 50 ppb is associated with increased risk of bladder, lung, and skin cancers. Small community water systems drawing from affected aquifers faced significant compliance costs when the 10 ppb standard took effect, and many small systems in rural Arizona, New Mexico, and Nevada struggled to finance the advanced treatment — reverse osmosis or activated alumina adsorption — required to meet the new standard. Arsenic MCL violations persist in small systems with limited technical and financial capacity to fund continuous treatment.

PFAS — per- and polyfluoroalkyl substances — represent the most significant expansion of SDWA regulation in decades. PFAS are a family of thousands of synthetic chemicals used in non-stick coatings, firefighting foam, food packaging, stain-resistant textiles, and industrial processes. They persist indefinitely in the environment and accumulate in human tissue; the two most widely studied compounds, PFOA and PFOS, are associated with kidney and testicular cancer, thyroid dysfunction, immune suppression, reproductive harm, and elevated cholesterol. In April 2024, the Biden EPA finalized the first-ever federal MCLs for PFAS in drinking water: 4 parts per trillion (ppt) each for PFOA and PFOS, which are among the lowest MCLs ever established for any contaminant and reflect an MCLG of zero (no safe level of exposure). The rule also established MCLs for PFNA, PFHxS, HFPO-DA (GenX), and a hazard index for mixtures. EPA estimated that between 66,000 and 80,000 public water systems would need to take action to comply with the new standards, with national compliance costs estimated at approximately $1.5 billion annually. Water systems have until 2027 to complete initial monitoring and until 2029 to comply with the MCLs, but the rule immediately triggers public notification requirements for systems with PFAS detections above the MCL. The PFAS MCL rule represents the most significant new drinking water regulatory action since the arsenic revision and is expected to generate substantial litigation.

Disinfection byproducts (DBPs) are chemical compounds formed when disinfectants — primarily chlorine — react with naturally occurring organic matter in source water. The two primary DBP families regulated under the SDWA are haloacetic acids (HAAs) and trihalomethanes (THMs), including chloroform. Both have been classified as probable human carcinogens based on animal studies and are associated with bladder cancer and, at very high exposures, adverse reproductive outcomes. The Stage 2 Disinfectants and Disinfection Byproducts Rule (2006) tightened the regulation of THMs and HAAs and introduced a locational running annual average (LRAA) compliance method that requires systems to evaluate compliance at each monitoring location rather than averaging across the distribution system, preventing utilities from diluting high-concentration monitoring sites with cleaner ones. DBP violations are most common in systems using surface water with high organic content — systems drawing from rivers or reservoirs with algae blooms or high natural organic matter — and in systems that rely on free chlorine rather than chloramine for secondary disinfection.

Radionuclides — including combined radium (Ra-226 and Ra-228), gross alpha particle activity, uranium, and beta/photon emitters — occur naturally in groundwater in areas with uranium-bearing geological formations, particularly in the Central Plains and parts of the Southeast. The radium MCL of 5 picocuries per liter (pCi/L) combined applies to Ra-226 plus Ra-228; the gross alpha MCL is 15 pCi/L. Radionuclide violations affect a small but persistent population of small groundwater systems that lack the financial and technical resources to install ion exchange or reverse osmosis treatment.

Coverage gaps: private wells and tribal water challenges

The Safe Drinking Water Act's most fundamental coverage gap is the explicit exclusion of private wells from federal regulation. Approximately 42 million Americans — roughly 13% of the US population — rely on private wells for their drinking water. These wells are not regulated under the SDWA, are not required to be tested for any contaminants, and fall entirely outside the SDWIS database. Their safety is the responsibility of the individual homeowner, who may have no knowledge of hydrogeology, no means to pay for water quality testing, and no recourse if a neighbor's activities contaminate the shared aquifer.

The geographic distribution of private well users overlaps substantially with the agricultural regions where nitrate and arsenic contamination are most prevalent. Studies by the US Geological Survey and the Centers for Disease Control have documented that a substantial fraction of private wells — estimates range from 10 to 25% depending on region and contaminant — exceed at least one federal health-based standard. Because these wells are not monitored, the exceedances go undetected and unreported. Private well owners who do test their water often do so only when purchasing a home and may not test for the full suite of regulated contaminants. EPA's authority to address private well contamination is limited to cases where a regulated facility caused the contamination, such as a Superfund site or a RCRA-regulated landfill.

Tribal water systems face a distinct set of challenges. Roughly half of all tribal water systems have unmet infrastructure needs, and tribal lands in arid regions — particularly the Navajo Nation in the Four Corners area — have historically faced severe water access constraints that go beyond regulatory compliance to include the absence of any piped water infrastructure at all. The Navajo Nation, the largest tribal land area in the United States, had more than 30% of households without running water as recently as the 2020 pandemic period, when the lack of handwashing infrastructure contributed to some of the highest COVID-19 infection rates in the country. Where tribal water systems do exist, they often serve small populations across vast geographic areas with aging infrastructure, limited technical capacity, and inadequate operations and maintenance funding. EPA's Indian Health Service and the USDA Rural Utilities Service provide capital grants for tribal water infrastructure, but the backlog of unmet needs substantially exceeds available funding.

Environmental justice: who bears the burden of water system violations

Academic research and investigative journalism have consistently documented that drinking water violations are not randomly distributed across the population but are concentrated in systems serving lower-income communities and communities of color. Research published in the Proceedings of the National Academy of Sciences by Switzer and Teodoro (2017) analyzed SDWIS violation data for the period 1982–2015 and found that race and ethnicity were significant predictors of Safe Drinking Water Act violations, even after controlling for system size, source water type, state, and income. Predominantly Hispanic communities had significantly higher rates of health-based violations than predominantly white communities. Similar disparities were documented for predominantly Black and Native American communities. The disparity was not explained by income alone: race remained a statistically significant predictor after controlling for poverty rates, suggesting that structural factors beyond simply resource constraints are at work.

The Environmental Working Group (EWG) maintains a public-facing tap water database at ewg.org that aggregates SDWIS violation data with utility-reported monitoring results and EWG's own health benchmarks, which are generally stricter than federal MCLs. The EWG database has been widely cited in media coverage of drinking water quality and provides a consumer-friendly interface for looking up a specific water utility's compliance history and contaminant detections. The Natural Resources Defense Council (NRDC) published a comprehensive analysis, “Threats on Tap,” documenting that more than 77 million Americans were served by water systems with at least one health-based violation during the period 2012–2017. A Reuters investigative series, “Off the Charts,” published in 2016–2017, used blood lead testing data and water system compliance records to document that the lead contamination problem was not unique to Flint but affected hundreds of school districts and water systems in predominantly low-income and minority communities across the country.

The systemic drivers of environmental justice disparities in drinking water quality include: the concentration of smaller and older water systems in rural and lower-income communities; the relationship between property values, tax base, and water utility revenue in systems that fund capital improvements through local rates; the historical underinvestment in water infrastructure in communities that were redlined or excluded from federal housing programs that channeled capital to suburban development; and the regulatory capacity constraints in primacy agencies that may apply less intensive oversight to systems whose constituents have less political influence.

The ECHO database: public access to SDWIS data

The EPA Enforcement and Compliance History Online (ECHO) platform, accessible at echo.epa.gov, is the primary public interface for SDWIS data. ECHO integrates drinking water compliance records from SDWIS with Clean Air Act, Clean Water Act, and RCRA compliance data, providing a unified facility-level compliance history view. For drinking water, ECHO provides:

The Safe Drinking Water System Search allows users to search for public water systems by name, city, state, county, PWSID (the unique seven-character identifier assigned to each public water system), or geographic area. Each system has a detail page showing its water source type (surface water, groundwater, purchased), population served, system type (CWS, NTNCWS, TNCWS), owner type, and a compliance summary. The compliance summary shows the number of violations in each category over recent years, active enforcement actions, and formal enforcement orders.

The SDWA compliance ratio — the percentage of regulated water systems in compliance with all health-based standards — is EPA's headline metric for national drinking water safety. EPA reports this metric annually in its Safe Drinking Water Act compliance reports. The FY2022 compliance ratio for health-based violations was approximately 92%, meaning roughly 8% of all systems had at least one health-based violation during the year. However, the compliance ratio is a count of systems, not a measure of the population affected: a large urban utility serving 1 million people has the same weight as a rural system serving 50 people. The population-weighted health-based violation rate is substantially lower than the system count rate because large systems, which serve most of the population, have far greater technical and financial resources to maintain compliance.

Significant noncompliance (SNC) is a SDWIS designation for systems with the most serious or persistent violations. The SNC definition includes systems with acute MCL violations (including E. coli), systems with health-based violations lasting more than one monitoring period without return to compliance, and systems that have failed to respond to state enforcement actions. EPA tracks SNC as a priority enforcement indicator; primacy states are expected to initiate formal enforcement action against all SNC systems within defined timeframes. EPA publishes quarterly snapshots of SNC systems by state in the ECHO database, and ECHO's state performance comparison tools allow researchers to identify states with persistently high SNC rates.

Bulk violation data is available for download from ECHO at echodata.epa.gov/echo/resource/docs/sdw_download_summary.zip, which provides quarterly snapshots of the national SDWIS dataset including system characteristics, violation history, enforcement actions, and formal agreements. The ECHO API, documented at echo.epa.gov/tools/web-services, provides programmatic access to system searches and violation queries with JSON output.

Enforcement mechanics: from notice of violation to consent order

SDWA enforcement follows a tiered escalation path. When a water system reports a violation — or when state monitoring data reveals an unacknowledged violation — the primacy state agency typically issues an initial notice of violationby letter. The notice identifies the specific regulation violated, the required corrective action, and the deadline for return to compliance. For minor monitoring violations, return to compliance may simply mean submitting the overdue monitoring results and paying a penalty. For MCL violations or treatment technique failures, the corrective action may require source water blending, treatment upgrades, or interim bottled water or point-of-use filter distribution.

If the water system fails to return to compliance within the required timeframe, the primacy agency may escalate to a formal enforcement action: an administrative order requiring specific corrective actions by specific dates, with penalties for noncompliance. EPA has authority under SDWA Section 1414 to issue administrative compliance orders and to assess civil penalties of up to $25,000 per day of violation. Criminal penalties under SDWA Section 1415 can be imposed for willful violations or for providing false information to regulators. For the most persistent or serious violations, EPA or the primacy state may enter a consent order — a negotiated legal agreement specifying the corrective actions, milestones, and penalties that govern the water system's return to compliance. Consent orders are public records and appear in the ECHO enforcement history.

The Water Infrastructure Improvements for the Nation (WIIN) Act of 2016, enacted in response to the Flint crisis, authorized dedicated funding for lead testing in schools and childcare facilities and for grants to small and disadvantaged water systems for infrastructure improvements and technical assistance. The Infrastructure Investment and Jobs Act (Bipartisan Infrastructure Law) of 2021 appropriated $15 billion specifically for replacing lead service lines and $10 billion for addressing PFAS and other emerging contaminants — the largest single federal investment in drinking water infrastructure in the history of the SDWA.

States with highest violation rates and systemic patterns

SDWIS data consistently shows that health-based violation rates are not uniform across states. Several structural factors predict high violation rates at the state level: a large number of very small water systems (which have fewer resources for compliance); predominance of groundwater sources (which may have elevated naturally occurring contaminants like arsenic, radium, or nitrate); a large agricultural sector that contributes to nitrate loading; and primacy agency capacity constraints that limit inspection frequency and enforcement speed.

States with historically high rates of health-based violations per system include Texas, which has an unusually large number of small community water systems in rural counties; New Mexico and Arizona, where arsenic in groundwater affects many small systems; and Pennsylvania, which has a large number of small municipal and non-community systems with aging infrastructure. California, which has the most public water systems of any state, also has a significant tail of small systems in agricultural regions with nitrate and arsenic compliance challenges, despite the California State Water Board's relatively aggressive enforcement posture.

Boil water orders are the most visible face of drinking water compliance failures: public advisories issued when microbial contamination is detected or when distribution system pressure losses or equipment failures create an acute risk of contamination. Boil water orders are issued by state or local health authorities based on monitoring data and engineering assessments. In the SDWIS context, they typically accompany public notification violations or immediate coliform MCL violations. EPA tracks the number of boil water orders issued annually as part of its national compliance monitoring but does not maintain a centralized federal database of all orders; boil water order records are primarily held at the state or local level.

Data access: SDWIS, ECHO API, and the Water Data Explorer

EPA makes SDWIS data accessible through several complementary channels suited to different levels of technical sophistication:

The Safe Drinking Water Search at sdwis.epa.gov provides a consumer- facing lookup for individual water systems. Users can enter a zip code, city, or water system name to find their utility and view its compliance history, system characteristics, and contact information. The search is designed for the general public rather than for bulk data analysis; it returns a system-level summary rather than record-level violation data.

The ECHO Drinking Water Search at echo.epa.gov/facilities/facility-search/sdwa provides more granular system-level queries with filters for state, violation status, system size, water source type, and SNC status. The ECHO interface returns a paginated list of systems matching the query criteria, with links to individual system detail pages showing full violation history, enforcement actions, and inspection records.

The ECHO API at echodata.epa.gov/echo/sdw_rest_services provides programmatic access to SDWIS data via HTTP GET requests with JSON output. The primary endpoints are sdw_rest_services.get_facilities for querying systems by geographic area, violation status, or system characteristics, andsdw_rest_services.get_facility_info for retrieving detailed violation and enforcement history for a specific PWSID. The API is documented at echo.epa.gov/tools/web-services/safe-drinking-water.

For bulk analysis, EPA's ECHO bulk downloads provide quarterly snapshots of the full SDWIS database in CSV format, available at the ECHO downloads page (echo.epa.gov/tools/data-downloads). The bulk download includes separate CSV files for system characteristics, violation records, enforcement actions, formal agreements, and inspection events. The violation file includes the PWSID, contaminant code, violation category, violation begin date, violation end date (populated when resolved), and the compliance status. The EPA Water Data Explorer provides a GIS visualization layer that overlays water system service areas with census demographic data, allowing environmental justice analysis without custom GIS software.

Python: querying the ECHO API for significant violations

The following script uses the EPA ECHO REST API to identify public water systems in Michigan that have current significant SDWA violations, returning basic facility information including population served and total violation count. Michigan is used as the example state because of its historical significance in the post-Flint regulatory landscape. The script requires only the standard requestsand pandas libraries and no API key — the ECHO API is publicly accessible without authentication.

import requests, pandas as pd

# EPA ECHO API — SDWA violations
# Docs: https://echo.epa.gov/tools/web-services/facility-search
base = "https://echodata.epa.gov/echo/sdw_rest_services.get_facilities"
params = {
    "output": "JSON",
    "p_violation_status": "Y",    # has violations
    "p_sdwis_vio_indicator": "Y", # significant violations
    "p_st": "MI",                  # Michigan (Flint example state)
    "p_act": "Y",                  # active systems
    "responseset": 20,
}
resp = requests.get(base, params=params, timeout=20)
data = resp.json()
results = data.get("Results", {}).get("Results", [])
print(f"Michigan water systems with significant SDWA violations: {len(results)} (sample)")
for r in results[:5]:
    pwsid     = r.get("RegistryID", "")
    name      = r.get("FacilityName", "")
    city      = r.get("LocationCity", "")
    viol_count = r.get("SDWViolations", "")
    pop       = r.get("PWSpopulationServed", "")
    print(f"  {name[:45]} ({city}) — Pop: {pop}, Violations: {viol_count}")

# SDWA violation summary statistics (from EPA enforcement data)
print("\n--- SDWA National Summary (FY2022) ---")
print("Public water systems (total):     ~150,000")
print("Community water systems:           ~51,000")
print("Systems serving >100K people:      ~1,200")
print("Systems in significant violation:  ~17,000")
print("Health-based violations:           ~6,800 systems")
print("Monitoring & reporting violations: ~12,000 systems")
print("Population affected by violations:  ~80M (one or more violation types)")

Several characteristics of the ECHO API are worth noting for production use. The responseset parameter limits the number of records returned in a single response; the API supports pagination via the qcolumnsand pageno parameters for larger result sets. Thep_sdwis_vio_indicator filter restricts results to systems with significant violations — the SNC-equivalent flag in ECHO — which are typically the highest-priority enforcement targets. Removing this filter returns all systems with any violation, which produces a much larger result set but includes many minor monitoring violations. The SDWViolationsfield in the response reflects total violation count across all violation types and monitoring periods; for health-based violation count specifically, thep_hv_viol parameter can be used to filter to systems with health-based violations only.

For national analysis, the bulk download is more practical than the API for large datasets. The violation CSV from the ECHO bulk download can be joined to the system characteristics CSV on PWSID to produce a flat file of violations with system attributes — population served, system type, primary source type, ownership type, state — that supports the multivariate analyses used in the environmental justice literature. The population-served field allows computing population-weighted violation rates that account for the fact that a single small system and a single large system receive equal weight in the raw system count compliance metrics that EPA reports publicly.