EWG's Tap Water Database: What's in your drinking water? (2023)

EWG's Tap Water Database: What's in your drinking water? (1)

November 2021

The EWG's Drinking Water Database contains information on the drinking water quality of nearly 50,000 municipal water systems across the country. The database provides information about chemical and radioactive contaminants found in drinking water and how those levels compare to legal limits and federal health guidelines. The EWG has been collecting and analyzing water quality data since 2003.

The 2021 edition of the database contains the results of water quality tests performed by water systems between 2014 and 2019. The EWG Drinking Water Quality Database totals nearly 31 million test results for 534 chemicals, 324 of which were found in drinking water. It is the largest source of free and open data on drinking water in the United States.

How EWG Collected the Data

State drinking water agencies, usually health or environment departments, maintain records of water test results from potable water systems or affiliated water testing laboratories. To build the database, the EWG requested test results from agencies responsible for monitoring drinking water quality in all 50 states and Washington, D.C.

In addition, the EWG obtained results from the Environmental Protection Agency testing drinking water for unregulated contaminants – substances known to contaminate drinking water but for which there are no national legal limits. The EPA's Third and Fourth Unregulated Contaminant Monitoring Rules (UCMR3and UCMR4) required municipal water systems serving more than 10,000 people to test water for 30 unregulated pollutants. Data collected from 2013 to 2016 for UCMR3 and from 2018 to 2021 for UCMR4 are included. The EWG database also includes information about drinking water violations from the EPA Enforcement and Compliance History Online orECO, website.

The EPA classifies water systems that purchase or receive some or all of their water from one or more municipal water systems as “consecutive systems', which have different water quality monitoring requirements. Such systems only need to be tested for disinfection by-products, lead and copper.

For successive systems, the EWG used publicly available records to list where the system would likely purchase its water and provide links to supply systems. If the slave system buys or receives water from only one utility, the EWG will list the water quality results for the utility on the slave system page.

For example, D.C. Water, which supplies tap water to the nation's capital, gets its water from the Washington Aqueduct, a US-affiliated state water agency. Army Corps of Engineers. Therefore, the Washington Aqueduct test results are also displayed on the pageWashington, DC, Wasser in der EWG Tap Water Database.

Population statistics for municipal water systems were obtained from state drinking water programs and supplemented with information from the US. EPA supplementedenvironmental factsData base. All population numbers are an estimate and the specific number of customers served by individual municipal water systems may vary.

(Video) EWG's Tap Water Database: What’s in Your Drinking Water?

The EWG database does not include water quality information for private wells because there are no federal regulations for testing private wells and data from private wells is not readily available.

Data quality control

After compiling our database, the EWG reviewed the data for inconsistencies and systematically sought, identified, and removed data points that could contain errors, such as: During this process, the EWG removed many thousands of test results flagged as potentially erroneous.

A few months before publication, the EWG informed theAssociation of State Drinking Water Managers, to dieAmerican Water Associationit's atAssociation of Municipal Water Authoritiesabout the next edition of the database. The EWG granted early access to the EWG database to the American Water Works Association and member companies of the Association of Metropolitan Water Agencies so that they could review and correct the data collected. For the release of the 2021 piped water database, water utilities took the opportunity to review data from their systems and then contacted the EWG during the review period to provide corrections, verify data accuracy, or suggest comments about the display of the data.

Calculation of the average pollutant content

For the 2021 edition of the EWG's Tap Water Database, the following time periods were used to calculate average contaminant concentrations for individual municipal water systems:

  • All samples are available for contaminants monitored in the EPA's UCMR3 and UCMR4 programs.
  • All samples for the 2014-2019 data period for radioactive elements.
  • All samples available for 2017-2019 for federally regulated water contaminants monitored annually and all other contaminants.

These periods were chosen to allow the EWG to collect information on occurrences of contaminants that are not monitored each year, such as: B. radiological contaminants, or chemicals that were monitored during a specific time period, such. B. UCMR3 contaminants.

For most pollutants, we selected three years of data from 2017 to 2019 to reflect the most recent pollutant concentrations.

The EWG calculated arithmetic mean pollutant concentrations for each municipal water system for the analyzed data period. Test results reported as "not recognized" were given a value of zero and included in the total data matrix to calculate averages.

This approach is conservative and has a negative impact on overall exposure estimates because, at least in some states, the limit of detection for reporting purposes is higher than achievable with the analytical capabilities of the most sensitive test methods.

(Video) How to use EWG's Tap Water Database to find out what's in your drinking water

In addition, all individual test results for each municipal water system are listed in the database for the 2014-2019 period and for the UCMR3 and UCMR4 programs. For each water sample, the EWG database listed the date, numerical result, and laboratory identification number, when available.

Some water systems mix water from different water sources in varying amounts, and this mixing can reduce the average amount of contaminants in finished tap water served to consumers. The water mix can be adjusted seasonally or more frequently, depending on overall water needs, supply changes and pollution levels. Water systems may use different averaging methods, and values ​​published in a water quality report may not necessarily match those in the database.

The EWG compared average pollutant concentrations calculated for individual municipal water systems to state and national population-weighted average pollutant concentrations for the same time period. State and national averages were calculated using the following formula:

EWG's Tap Water Database: What's in your drinking water? (2)

where the average pollutant concentration corresponds to values ​​for individual municipal water systems of different sizes; Total population is the population served by municipal water supply systems at national or national level; and the resulting values ​​are summed for all municipal water systems within a state or nationally. This average includes systems where pollutants were listed as undetected. These systems were treated as if they had zero pollution for the calculation of population weighted averages.

health guidelines

The EWG compared average pollutant concentrations to legal limits and federal health guidelines published by government agencies and the EWG's own research:

  • EPA or MCL Maximum Contaminant Level - the federally enforceable standard that defines the highest level of contaminants allowed in drinking water. The EPA hasn't set a new tap water standard in nearly 20 years. Among existing MCLs for chemical contaminants, two are over 40 years old (MCLs for nitrate and radium); eight were released in 1987 and most were developed in the early 1990s.available here.
  • California Public Health Objective, or PHG – defined by the California Office of Environmental Health Hazard Assessment, or OEHHA, as the level of contaminant in drinking water that does not pose a significant health risk when consumed over a lifetime. Public health goals are based solely on health outcomes. For carcinogens, the level is equivalent to one extra case of cancer for every million people who drink water in their lifetime.available here.
  • EPA One in a Million Cancer Risk Level – the concentration of a chemical in drinking water that equates to an estimated lifetime risk of cancer in one million, as published by the EPA Integrated Risk Information System.available here.
  • EPA's Unregulated Contaminant Monitoring Program Reference Level – an unenforceable drinking water contaminant health guideline that provides a baseline for unregulated contaminants included in the EPA's Monitoring Program.available here.
  • Minnesota Health Hazard Limit – defined by the Minnesota Department of Health as the concentration of a groundwater contaminant or mixture of contaminants that can be consumed with little or no health risk.available here.
  • EWG Standards - Health guidelines developed by the EWG based on the latest scientific research.available here.

Unenforceable health guidelines represent the maximum concentration of a contaminant in water that scientists believe is safe. This figure is based on health protection only and does not take into account treatment costs, treatment feasibility or other factors.

For chemicals that can cause cancer, health guidelines generally represent one extra case of cancer for every million people who drink water in their lifetime. For chemicals that are not considered carcinogenic, health guidelines are established using toxicity information from animal or human studies after applying additional safety factors.

These safety factors are used to provide a margin of safety based on differences between humans and animals, differences between individuals in their susceptibility to chemical exposure, and general uncertainty - the fact that for many chemicals, scientists do not fully understand the possible health effects. In addition, safety factors often include the increased likelihood of harm from exposure to toxic chemicals during pregnancy or childhood.

(Video) EWG's Tap Water Standards

Most of the health guidelines in the database reflect public health goals published by the OEHHA. Where multiple health-based guidelines are available, the EWG used the most recent health assessments performed by federal or state health agencies.

Exposure to pollutants at levels above health guidelines increases the possibility of additional adverse health effects. For chemicals with health guidelines, we have identified a critical health effect and a list of other health effects observed in research studies. The primary sources of information for other health effects were drinking water toxicity assessments conducted by the State of California or the EPA.

EPA published additionallyMaximum pollution targets, or MCLG, along with the MCLs for individual chemicals. MCLGs are unenforceable federal health guidelines. For cancer-causing chemicals, the EPA typically sets these health targets to zero.

The EPA has published zero MCLGs for acrylamide, alachlor, arsenic, benzene, benzo[a]pyrene (PAHs), bromate, bromodichloromethane, bromoform, carbon tetrachloride, chlordane, 1,2-dibromo-3-chloropropane, 1,2- Dichloroethane, Dichloromethane, 1,2-Dichloropropane, Di(2-ethylhexyl)phthalate, Dioxin (2,3,7,8-TCDD), Epichlorohydrin, Ethylene Dibromide, Heptachlor, Hexachlorobenzene, Lead, PCBs, Pentachlorophenol, Tetrachloroethylene, Toxaphene , Trichlorethylene , Vinyl chloride, alpha particles, beta particles, radium and uranium.

View lead test results

Water companies test for lead and copper levels in their customers' homes, as opposed to testing for other contaminants, to account for the fact that corrosion and lead leaching occurs in water pipes and domestic plumbing. Lead test results indicate the potential level of lead hazards in a water system, but do not reliably predict specific lead levels for tap water in individual homes. For this reason, the EWG displays individual lead test results and 90th percentile lead test values ​​when available.

The EPA's current lead and copper rule allows 10 percent of sampled households to exceed the federal lead action level of 15 parts per billion, or ppb; Ninety percent of sampled homes must have a lead level of less than 15 ppb for the municipal water system to meet federal regulations. The EWG obtained information on 90th percentile lead tests from the EPA's Envirofacts database and displayed data for the most recent years available.

Water utilities also report individual test results to government agencies responsible for monitoring the safety of drinking water in each state. The EWG collected lead test results from individual households when available and displayed this information in our database. Whenever a water system has tested at least 10 domestic water samples for lead in the most recent year analyzed by the EWG, the test results are displayed in a pie chart to help viewers distinguish the proportion of tests above health guidelines .

EWG analysis of drinking water compliance data

To test whether tap water provided by various municipal water systems meets federal drinking water standards, the EWG reviewed information from EPAs.ECODatabase for the most recent three-month period for which the EPA has published assessment information online, as well as information about the system's compliance status over the past three years.

(Video) EWG's 2019 Tap Water Database

Drinking water quality is regulated at the state level, with state agencies in all but one state responsible for compiling and verifying drinking water data, confirming that municipal water systems comply with federal laws, and addressing water quality issues. non-compliance through inspection actions.

Wyoming is an exception, as the EPA's regional office is directly responsible for overseeing the state's potable water systems. Drinking water systems collect and report water quality data to appropriate authorities, and information about violations of the Safe Drinking Water Act is compiled and reported to EPA authorities on a quarterly basis.

The EPA describes theCompliance Process with the Safe Drinking Water Actas follows:

Once a breach is reported, it typically takes three to six months for the official quarterly status of the [public water system] to be updated. The most recent "official" compliance status is shown in the Q12 asset breakdown report. If states provide new information on violations for the next quarter, those violations will appear in Q13. Until the next quarter becomes official, these data are considered drafts, are not fully guaranteed and are subject to change.

Sedefined by EPA, there are several types of drinking water violations, the most serious being a health violation, which indicates failure to comply with federal MCLs or other legal requirements that limit levels of contaminants in water, such as proper lead treatment techniques. The EPA awards a higher number of violations – five or ten – for such significant compliance issues.

Other types of violations include monitoring and reporting violations, violating public service announcements, and failing to maintain mandatory water treatment records. These compliance issues are usually assigned a point of violation.

Violation points are accrued for that system based on its compliance history and remain assigned to that system until specific violations are corrected. The EPAsECHO database help pageexplains the types of health-related violations, other types of violations, and the weighted scoring system the EPA uses to reflect a water system's level of noncompliance.

In addition to identifying specific violations, EPA identifies municipal water systems with severe, multiple, and/or persistent unresolved violations. Such systems are designated as “serious infractions” so that the drinking water system and the responsible authority can act quickly to correct the problem. Formal enforcement action may be taken where provided by law.

The EPA's ECHO website also contains detailed information about the plant, which can be accessed via the link at the bottom of any water system page in the EWG Tap Water Database. This detailed asset report includes a summary chart for the last 12 quarters, with each quarter flagged as non-violation, non-compliance, material violation or unknown. These reports also include detailed violations for each quarter and regulation of drinking water quality. In the EPA's summary charts for the detailed facility reports, quarters of violations are classified as "non-compliance" and quarters of serious violations are classified as "serious violations".

EWG tap water database pages for individual water systems indicate "yes" or "no" whether the system was listed by the EPA as "in violation" or "a serious violation" in the last three years of revised data. Where information was available, the EWG also listed the number of quarters in the last three years that a given water system was described as having "violated" or "severely violated" drinking water standards. State pages in the database rank municipal water systems in violation by the number of current violations not corrected, according to information available on the ECHO website.

(Video) EWG Explains: Radium in tap water


The EWG worked to ensure the accuracy of the information provided in the Drinking Water Database. The database is dynamic. Instructions for use, contamination levels and other information in the database may change based on evolving scientific knowledge, new information or other factors. Please note that the database generally relies on data drawn from various sources and therefore EWG cannot guarantee the accuracy of the information provided or any analysis based on it.

The EWG database is provided for your personal, non-commercial use only. It is intended to help consumers make informed choices about their health and environment. Please note that all information that the EWG makes available through the database is for general informational purposes only and is not intended to, nor should it be relied on, as a substitute for professional medical advice. The full EWG Terms and Conditions can be found hereHere.


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