EWG's Tap Water Database — 2021 UPDATE

Science Lab

Developing health-protective standards for drinking water

EWG issues no-compromise benchmarks for removing water contaminants

November 2021

When it comes to drinking water, a passing grade from the government does not necessarily mean the water is safe.

Federal drinking water standards have not been updated in decades, and the regulatory process does not take into consideration the heightened vulnerability to toxic chemicals of children, infants and the developing fetus. Many chemicals known to pose risks lack enforceable federal health standards, leaving the public susceptible to harm from new and emerging contaminants in tap water.

EWG standards are not based on compromises polluters and politicians find acceptable, or the cost of cleaning up drinking water supplies. Rather, to arrive at these standards, EWG reviewed the best and latest scientific evidence, legal standards and health advisories, and then we defined water quality goals that will truly protect public health. The fifth edition of EWG’s national Tap Water Database applies no-compromise standards for water contaminants that have no federal legal limit or that have legal limits too weak to ensure safe water quality.


Federal legal limit (parts per billion or parts per million)

EWG-recommended health guideline

Health effects


3 ppb

0.1 ppb

Hormone disruption; cancer; harm to the developing fetus and reproductive system; changes in the nervous system, brain and behavior


2 ppm

0.7 ppm

High blood pressure; harm to the kidneys, heart and blood vessels


700 ppb

5 ppb

Cancer; harm to fetal growth and the kidneys


10 ppm

0.14 ppm

Cancer; harm to fetal growth and child development



0.001 ppb

Cancer; hormone disruption; harm to fetal growth, child development, the immune system and liver



0.007 ppt

Cancer; hormone disruption; harm to fetal growth, child development, the immune system and liver


80 ppb

0.15 ppb

Bladder and skin cancer, harm to fetal growth and development

To see all EWG standards, click here .

How EWG developed the standards

As new EWG standards are developed, they will be added to this list.


EWG scientists used the latest epidemiological data to define a health-protective benchmark for atrazine exposure during the critical period of pregnancy, when the developing fetus is most vulnerable to the effects of hormone-disrupting chemicals.

Our calculations started with an atrazine concentration of 1 part per billion, or ppb, which studies associate with a greater risk of preterm birth, and include an additional tenfold safety factor, which is supported by the federal Food Quality Protection Act . This approach results in a concentration of no more than 0.1 ppb for atrazine, simazine and related herbicides, whether present alone or in combination.

For more information, see the EWG report "Hormone-Disrupting Weed Killer Taints Drinking Water for Millions of Americans."


EWG scientists defined a health benchmark of 0.7 parts per million, or ppm, for barium in drinking water, to protect against harm to the kidneys and the cardiovascular system. This benchmark was based on studies by the federal Agency for Toxic Substances and Disease Registry and the California Office of Environmental Health Hazard Assessment, with the inclusion of a tenfold children’s health safety factor.


EWG scientists developed a health benchmark for glyphosate to protect against the risk of cancer. Calculations started from a No Significant Risk Level – the amount not expected to raise the cancer risk resulting from a lifetime of exposure – of no more than 10 micrograms per day. This amount is divided by an estimated average of two liters of drinking water consumed each day, which results in a limit of no more than 5 micrograms per liter, the equivalent of 5 ppb.

For more information, see "California Proposes Safe Level for Roundup More Than 100 Times Lower Than EPA Limit."


EWG scientists defined a health benchmark of 0.14 ppm for nitrate, as well as for the combined level of nitrate and nitrite. This benchmark corresponds to a one-in-a-million annual cancer risk level, and it also protects against harm to the developing fetus.

For more information, see our report and peer-reviewed scientific study “Exposure-Based Assessment and Economic Valuation of Adverse Birth Outcomes and Cancer Risk Due to Nitrate in United States Drinking Water.”

Toxic fluorinated compounds, or PFAS

EWG scientists defined a health benchmark of 1 part per trillion, or ppt, for the total concentration of all PFAS that may occur in drinking water. This benchmark protects against harm that these fluorinated compounds can cause to the immune system and the risks of various chronic diseases.

For more information, see "EWG Proposes PFAS Standards That Fully Protect Children’s Health."


EWG scientists defined a health benchmark of 0.007 parts per trillion, or ppt, specifically for PFOA, to protect against kidney cancer, liver damage and other health risks, including harm to the immune system. This guideline for PFOA was proposed in 2021 by the California Office of Environmental Health Hazard Assessment as a draft public health goal.


EWG scientists defined a health benchmark of 0.15 ppb for four trihalomethanes1 as a group, or THM4. The Environmental Protection Agency calls this group total trihalomethanes, or TTHM. The EWG health benchmark represents a lifetime one-in-a-million cancer risk level benchmark for the THM4/TTHM group.

For more information, see the report and the EWG peer-reviewed scientific article “Cumulative Risk Analysis of Carcinogenic Contaminants in United States Drinking Water.”

1 Chloroform, bromoform, dibromochloromethane and bromodichloromethane.