When it comes to drinking water, a passing grade from the government does not necessarily mean the water is safe.
The Environmental Protection Agency hasn’t updated most of its drinking water standards in decades. And its process for setting them doesn’t consider 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.
To help people understand the limitations of the federal oversight of drinking water, EWG has devised its own health-based guidelines for water contaminants that either have no federal legal limits or that have legal limits too weak to ensure drinking water is safe.
Unlike many federal limits, EWG standards are not based on compromises that polluters and politicians find acceptable, or on what it will cost to clean up drinking water supplies. Industries often push back on improving water quality by claiming that it would be too expensive, ignoring the health benefits of removing harmful contaminants from tap water.
In developing these standards, EWG scientists reviewed the best and latest scientific evidence, legal standards and health advisories. Then they defined water quality goals that will truly protect public health.
Below are some examples of EWG’s health-based standards, for some of the most commonly found contaminants in tap water. To see the entire list, click here.
| Contaminant | Federal legal limit (parts per billion or parts per million) | EWG-recommended health guideline | Health effects |
|---|---|---|---|
| Atrazine | 3 ppb | 0.1 ppb | Hormone disruption; cancer; harm to the developing fetus and reproductive system; changes in the nervous system, brain and behavior |
| Barium | 2 ppm | 0.7 ppm | High blood pressure; harm to the kidneys, heart and blood vessels |
| Glyphosate | 700 ppb | 5 ppb | Cancer; harm to fetal growth and the kidneys |
| Nitrate | 10 ppm | 0.14 ppm | Cancer; harm to fetal growth and child development |
| PFOS | 4 ppt | 0.03 ppt | Cardiovascular harm; harm to fetal growth |
| PFOA | 4 ppt | 0.09 ppt | Harm to fetal growth, child development, the immune system; increased cholesterol |
| Trihalomethanes | 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 updated and 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.
The 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 EWG’s 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 “forever chemicals,” or PFAS
EWG scientists defined a health benchmark of 0.3 part per trillion, or ppt, specifically for PFOS – one of the most-studied and notorious PFAS – to protect against cardiovascular harm and harm to fetal growth. The health benchmark is also set to be protective of liver damage and harm to the immune system. This value is based on the final toxicity value published in a health assessment by the EPA’s Office of Water.
EWG scientists defined a health benchmark of 0.09 parts per trillion, or ppt, specifically for the forever chemical PFOA, to protect against harm to the immune system, decreased birth weight and increased cholesterol. This final toxicity value was published in a health assessment by the EPA’s Office of Water.
Trihalomethanes (TTHMs)
EWG scientists defined a health benchmark of 0.15 ppb for four trihalomethanes (chloroform, bromoform, dibromochloromethane and bromodichloromethane) as a group, or THM4. The EPA 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.”
February 2025