EWG's Tap Water Database — 2019 UPDATE

Science Lab

EWG Standards for Drinking Water Contaminants

October 2019

No-compromise benchmarks to fully protect public health

When it comes to drinking water, getting 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 fourth edition of EWG’s National Tap Water Database sets forth no-compromise standards for water contaminants that have no federal legal limit or that have legal limits too weak to ensure safe water quality.

ContaminantFederal Legal Limit (parts per billion or parts per million)EWG-recommended health guidelineHealth Effects
Atrazine3 ppb0.1 ppbHormone disruption; cancer; harm to the developing fetus and reproductive system; changes in the nervous system, brain and behavior
Barium2 ppm0.7 ppmHigh blood pressure; harm to the kidneys, heart and blood vessels
Glyphosate700 ppb5 ppbCancer; harm to fetal growth and the kidneys
Nitrate10 ppm0.14 ppmCancer; harm to fetal growth and child development
PFASNonexistent0.001 ppbCancer; hormone disruption; harm to fetal growth, child development, the immune system and liver
Trihalomethanes80 ppb0.15 ppbBladder 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 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 parts per million, or ppm, for nitrate, as well as for the combined level of nitrate and nitrite. This benchmark corresponds to a one-in-one-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 0.15 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-one-million cancer risk level benchmark for the THM4/TTHM group.

For more information, see the EWG peer-reviewed scientific article “Cumulative risk analysis of carcinogenic contaminants in United States drinking water.”

1 Chloroform, bromoform, dibromochloromethane and bromodichloromethane.