EWG’s health standards listed in the Tap Water Database represent the maximum concentration of a contaminant in water that scientists consider safe. This value is based only on protecting health and does not consider technical feasibility or the cost of water treatment.
The following table includes health guidelines published by federal or state health and environmental agencies, or developed by EWG scientists based on the best and most recent research.
More details on health guideline selections are available in the data sources and methodology sections.
Units used in the table: parts per million, or ppm; parts per billion, or ppb; and picocuries per liter, or pCi/L.
Updated February 2025
| Contaminant (in alphabetical order) | Environmental Protection Agency limit | EWG standard | Source of EWG standard | Contaminant’s health effects |
|---|---|---|---|---|
| 1,1-Dichloroethane | Nonexistent | 3 ppb | California public health goal | Cancer; change to the heart and blood vessels |
| 1,1,2-Trichloroethane | 5 ppb | 0.3 ppb | California public health goal | Liver cancer; harm to the kidney; change to the central nervous system |
| 1,2-Dibromo-3- chloropropane | 0.2 ppb | 0.0017 ppb | California public health goal | Testicular cancer; harm to the male reproductive system; infertility |
| 1,2-Dichloroethane | 5 ppb | 0.4 ppb | California public health goal |
Cancer; harm to the immune system; harm to the stomach and intestines; harm to the liver; harm to the kidney; harm to the brain and nervous system |
| 1,2-Dichloropropane | 5 ppb | 0.5 ppb | California public health goal | Liver cancer; harm to the liver; harm to the kidney; change to blood cells |
| 1,2,3-Trichloropropane | Nonexistent | 0.0007 ppb | California public health goal | Cancer |
| 1,2,4-Trichlorobenzene | 70 ppb | 5 ppb | California public health goal | Harm to the adrenal gland; cancer |
| 1,3-Butadiene | Nonexistent | 0.0103 ppb | Contaminant concentration corresponding to a one- in-a-million lifetime risk of cancer, as defined by the Environmental Protection Agency | Cancer; harm to the brain and nervous system; harm to reproduction and child development; change to blood cells; change to the kidney |
| 1,4-Dioxane | Nonexistent | 0.35 ppb | Contaminant concentration corresponding to a one- in-a-million lifetime risk of cancer, as defined by the Environmental Protection Agency | Cancer; irritation of the lungs; harm to the kidney |
| p-Dichlorobenzene | 75 ppb | 6 ppb | California public health goal |
Cancer; harm to the liver; harm to the kidney; harm to the thyroid |
| 2,4-D (2,4-dichlorophenoxyacetic acid) | 70 ppb | 20 ppb | California public health goal |
Hormone disruption; harm to the liver; harm to the kidney; harm to the thyroid; harm to
the brain and nervous system; change to immune system function |
| Aluminum | Nonexistent | 600 ppb | California public health goal | Harm to the brain and nervous system |
| Antimony | 6 ppb | 1 ppb | California public health goal | Harm to the liver; change to the stomach and intestines |
| Arsenic | 10 ppb | 0.004 ppb | California public health goal |
Cancer; harm to the central nervous system; harm to the brain and nervous system; skin
damage; change to the heart and blood vessels; increase the risk of heart disease, stroke and diabetes |
| Atrazine | 3 ppb | 0.1 ppb | EWG-recommended health guideline | Harm to the developing fetus; hormone disruption; harm to the reproductive system; changes in the nervous system; changes in brain and behavior; cancer |
| Barium | 2 ppm | 0.7 ppm | Children's health- based limit for 10-day exposure, as defined by the Environmental Protection Agency | Harm to the kidney; high blood pressure; harm to the heart and blood vessels |
| Benzene | 5 ppb | 0.15 ppb | California public health goal | Cancer; harm to blood cells; harm to the central nervous system; harm to child development; harm to the immune system |
| Benzo[a]pyrene | 0.2 ppb | 0.007 ppb | California public health goal | Cancer; harm to the immune system; harm to reproduction and child development; change to the central nervous system |
| Beryllium | 4 ppb | 1 ppb | California public health goal | Harm to the stomach and intestines; harm to the lungs; harm to bones |
| Bromate | 10 ppb | 0.1 ppb | California public health goal | Cancer |
| Bromochloroacetic acid | Nonexistent | 0.02 ppb | EWG-recommended health guideline | Cancer; harm to fetal growth and development. |
| Bromodichloroacetic acid | Nonexistent | 0.04 ppb | EWG-recommended health guideline | Cancer; harm to fetal growth and development. |
| Bromodichloromethane | Nonexistent | 0.06 ppb | California public health goal |
Cancer; harm to reproduction and child development; change to fetal growth and development |
| Bromoform | Nonexistent | 0.5 ppb | California public health goal |
Cancer; harm to reproduction and child development; change to fetal growth and development |
| Cadmium | 5 ppb | 0.04 ppb | California public health goal | Cancer; harm to the kidney; change in behavior |
| Carbofuran | 40 ppb | 0.7 ppb | California public health goal | Harm to the brain and nervous system; harm to the reproductive system |
| Carbon tetrachloride | 5 ppb | 0.1 ppb | California public health goal | Cancer; harm to the liver; harm to the central nervous system; harm to the kidney; decrease in fertility |
| Chlorate | Nonexistent | 210 ppb | Health benchmark defined by the Environmental Protection Agency for testing under the Unregulated Contaminant Monitoring Rule program | Hormone disruption |
| Chlordane | 2 ppb | 0.03 ppb | California public health goal | Cancer; hormone disruption; harm to reproduction and child development |
| Chlorodibromoacetic acid | Nonexistent | 0.02 ppb | EWG-recommended health guideline | Cancer; harm to fetal growth and development |
| Chlorite | 1 ppm | 0.050 ppm | California public health goal | Change to blood cells; change to the thyroid; hormone disruption; harm to reproduction and child development |
| Chloroform | Nonexistent | 0.4 ppb | California public health goal | Cancer; harm to fetal growth and development |
| Chloromethane | Nonexistent | 2.69 ppb | Health benchmark defined by the Environmental Protection Agency for testing under the Unregulated Contaminant Monitoring Rule program | Cancer |
| Chromium (hexavalent) | Nonexistent | 0.02 ppb | California public health goal | Cancer; harm to the liver; harm to the reproductive system |
| Cobalt | Nonexistent | 70 ppb | Health benchmark defined by the Environmental Protection Agency for testing under the Unregulated Contaminant Monitoring Rule program | Harm to the heart; change in blood chemistry; harm to the stomach and intestines |
| Copper | Nonexistent | 300 ppb | California public health goal | Diarrhea; weight loss; vomiting |
| Cyanide | 200 ppb | 150 ppb | California public health goal | Harm to the brain and nervous system; harm to the thyroid; harm to the central nervous system |
| Di(2-ethylhexyl) adipate | 400 ppb | 200 ppb | California public health goal | Change to fetal growth and development; harm to the liver |
| Di(2-ethylhexyl) phthalate | 6 ppb | 3 ppb | Contaminant concentration corresponding to a one- in-a-million lifetime risk of cancer, as defined by the Environmental Protection Agency | Harm to the male reproductive system; harm to the immune system; change to fetal growth and development; hormone disruption |
| Dibromoacetic acid | Nonexistent | 0.03 ppb | California public health goal | Cancer; harm to fetal growth and development |
| Dibromochloromethane | Nonexistent | 0.1 ppb | California public health goal | Cancer; harm to fetal growth and development |
| Dichloroacetic acid | Nonexistent | 0.2 ppb | California public health goal | Cancer; harm to reproduction and child development |
| p-Dichlorobenzene | 75 ppb | 6 ppb | California public health goal | Cancer; harm to the liver; harm to the kidney; harm to the thyroid |
| Dichloromethane (methylene chloride) | 5 ppb | 4 ppb | California public health goal | Cancer; harm to reproduction and child development; harm to the liver |
| Diquat | 20 ppb | 6 ppb | California public health goal | Change to fetal growth and development; change in body weight; harm to the kidney; cataracts |
| Endothall | 100 ppb | 94 ppb | California public health goal | Change to the stomach and intestines; eye damage; skin irritation |
| Endrin | 2 ppb | 0.3 ppb | California public health goal | Cancer; change to the central nervous system; harm to the immune system; harm to the reproductive system |
| Ethylbenzene | 700 ppb | 300 ppb | California public health goal | Cancer; harm to the lungs; harm to the liver; harm to the kidney; change to the central nervous system |
| Ethylene dibromide | 0.05 ppb | 0.01 ppb | California public health goal | Cancer; harm to the reproductive system; harm to the central nervous system; change to fetal growth and development |
| Glyphosate | 700 ppb | 5 ppb | EWG-recommended health guideline |
Cancer; harm to fetal growth; harm to the kidney |
| Haloacetic acids (HAA5) | 60 ppb | 0.1 ppb | EWG-recommended health guideline | Cancer; harm to fetal growth and development |
| Heptachlor | 0.4 ppb | 0.008 ppb | California public health goal | Cancer; hormone disruption; harm to the brain and nervous system |
| Heptachlor epoxide | 0.2 ppb | 0.006 ppb | California public health goal | Cancer; hormone disruption; harm to the liver |
| Hexachlorobenzene | 1 ppb | 0.03 ppb | California public health goal | Cancer; harm to the brain and nervous system; hormone disruption |
| Hexachlorocyclopentadiene | 50 ppb | 2 ppb | California public health goal | Harm to the stomach and intestines; change to the liver; change to the kidney; irritation of the lungs |
| Hexafluoropropylene oxide dimer acid (HFPO-DA) | 10 ppt and Hazard Index* | 9 ppt | EPA’s Human Health toxicity value | Harm to the liver |
| Lead | 10 ppb (federal action level for lead in drinking water)** | 0.2 ppb | California public health goal | Harm to the brain and nervous system |
| Lindane | 0.2 ppb | 0.032 ppb | California public health goal | Cancer; harm to the brain and nervous system; harm to the immune system |
| Manganese | Nonexistent | 100 ppb | A risk assessment advisory level defined by the Minnesota Department of Health | Harm to the brain and nervous system; change in behavior |
| Mercury (inorganic) | 2 ppb | 1.2 ppb | California public health goal | Harm to the brain and nervous system; harm to fetal growth and child development; harm to the kidney; harm to the immune system |
| Methoxychlor | 40 ppb | 0.09 ppb | California public health goal | Hormone disruption; harm to the reproductive system; harm to the kidney; harm to the liver; harm to the immune system; harm to the brain and nervous system |
| Molybdenum | Nonexistent | 40 ppb | The Environmental Protection Agency health advisory for lifetime exposure | Change in blood chemistry; gout |
| Monobromoacetic acid | Nonexistent | 25 ppb | California public health goal | Change to fetal growth and development |
| Monochloroacetic acid | Nonexistent | 53 ppb | California public health goal | Change to fetal growth and development |
| Monochlorobenzene (chlorobenzene) | 100 ppb | 70 ppb | California public health goal | Harm to the liver; harm to the kidney |
| MTBE | Nonexistent | 13 ppb | California public health goal | Cancer |
| N-Nitrosodimethylamine (NDMA) | Nonexistent | 0.003 ppb | California public health goal | Cancer |
| Nitrate (measured as Nitrogen) | 10 ppm | 0.14 ppm | EWG-recommended health guideline | Cancer; harm to fetal growth and child development |
| Oxamyl | 200 ppb | 26 ppb | California public health goal |
Harm to the central nervous system; harm to the brain and nervous system; harm to child development |
| Pentachlorophenol | 1 ppb | 0.3 ppb | California public health goal | Cancer; harm to child development; harm to the immune system; hormone disruption |
| Perchlorate | Nonexistent | 1 ppb | California public health goal | Hormone disruption; harm to fetal growth and child development |
| Perfluorobutane sulfonate (PFBS) | Hazard Index* | 2 ppb | EPA’s Human Health toxicity value | Hormone disruption; harm to fetal growth and child development |
| Perfluorobutanoic acid (PFBA) | Nonexistant | 1 ppb | EPA recommended application of the toxicity value for PFHxA published in the Integrated Risk Information System’s toxicological review | Harm to fetal growth and child development |
| Perfluorodecanoic acid (PFDA) | Nonexistant | 0.006 ppt | EPA toxicity value published in the Integrated Risk Information System’s toxicological review | Harm to the immune system; harm to fetal growth and child development |
| Perfluorodecanesulfonic acid (PFDS) | Nonexistant | 0.001 ppt | EPA recommended application of the PFHxS toxicity value published in Integrated Risk Information System toxicological review | Harm to the developing immune system |
| Perfluorododecanoic acid (PFDoA) | Nonexistant | 0.006 ppt | EPA recommended application of the toxicity value for PFDA published in the Integrated Risk Information System’s toxicological review | Harm to the immune system; harm to fetal growth and child development |
| Perfluoroheptanoic acid (PFHPA) | Nonexistent | 1 ppb | EPA recommended application of the toxicity value for PFHxA published in the Integrated Risk Information System’s toxicological review | Harm to fetal growth and child development |
| Perfluoroheptane sulfonic acid (PFHpS) | Nonexistent | 0.001 ppt | EPA recommended application of the PFHxS toxicity value published in Integrated Risk Information System toxicological review | Harm to the developing immune system |
| Perfluorohexane sulfonate (PFHXS) | 10 ppt and Hazard Index* | 0.001 ppt | EPA toxicity value published in Integrated Risk Information System toxicological review | Harm to the developing immune system |
| Perfluorohexanoic acid (PFHxA) | Nonexistant | 1 ppb | EPA toxicity value published in Integrated Risk Information System toxicological review | Harm to fetal growth and child development |
| Perfluorononanoic acid (PFNA) | 10 ppt and Hazard Index* | 0.006 ppb | EPA recommended application of the toxicity value for PFDA published in the Integrated Risk Information System’s toxicological review | Harm to the immune system; harm to fetal growth and child development |
| Perfluorooctane sulfonate (PFOS) | 4 ppt | 0.3 ppt | EPA final toxicity value from the Office of Water’s Final Human Health Toxicity Assessment | Cardiovascular harm; harm to fetal growth |
| Perfluorooctanesulfonamide (PFOSA) | Nonexistent | 0.3 ppt | EPA final toxicity value for PFOS from the Office of Water’s Final Human Health Toxicity Assessment | Cardiovascular harm; harm to fetal growth |
| Perfluorooctanoic acid (PFOA) | 4 ppt | 0.09 ppt | EPA final toxicity value from the Office of Water’s Final Human Health Toxicity Assessment | Harm to the immune system; harm to fetal growth and child development; increased cholesterol |
| Perfluoropentanoic Acid (PFPeA) | Nonexistent | 1 ppb | EPA recommended application of the toxicity value for PFHxA published in the Integrated Risk Information System’s toxicological review | Harm to fetal growth and child development |
| Perfluorotetradecanoic acid (PFTA) | Nonexistent | 0.006 ppt | EPA recommended application of the toxicity value for PFDA published in the Integrated Risk Information System’s toxicological review | Harm to the immune system; harm to fetal growth and child development |
| Perfluorotridecanoic acid (PFTrDA) | Nonexistent | 0.006 ppt | EPA recommended application of the toxicity value for PFDA published in the Integrated Risk Information System’s toxicological review | Harm to the immune system; harm to fetal growth and child development |
| Perfluoroundecanoic acid (PFUnA) | Nonexistent | 0.006 ppt | EPA recommended application of the toxicity value for PFDA published in the Integrated Risk Information System’s toxicological review | Harm to the immune system; harm to fetal growth and child development |
| Picloram | 500 ppb | 166 ppb | California public health goal | Harm to the liver; harm to the kidney; change to the reproductive system |
| Polychlorinated biphenyls (PCBs) | 0.5 ppb | 0.09 ppb | California public health goal | Breast cancer; prostate cancer; harm to the brain and nervous system; hormone disruption; harm to the immune system |
| Radium-226 |
5 pCi/L for combined radium-226 and radium-228 |
0.05 pCi/L | California public health goal | Cancer |
| Radium-228 |
5 pCi/L for combined radium-226 and radium-228 |
0.019 pCi/L | California public health goal | Cancer |
| Selenium | 50 ppb | 30 ppb | California public health goal | Hormone disruption; harm to child development; harm to the brain and nervous system; skin damage |
| Simazine | 4 ppb | 0.1 ppb | EWG-recommended health guideline | Harm to the developing fetus; hormone disruption; harm to the reproductive system; changes in the nervous system; changes in brain and behavior; cancer |
| Strontium | Nonexistent | 1.5 ppm | Health benchmark defined by the Environmental Protection Agency for testing under the Unregulated Contaminant Monitoring Rule program | Harm to bones |
| Strontium-90 | Nonexistent | 0.35 pCi/L | California public health goal | Cancer; harm to bones |
| Styrene | 100 ppb | 0.5 ppb | California public health goal | Cancer; harm to the liver; harm to the brain and nervous system |
| Tetrachloroethylene (perchloroethylene) | 5 ppb | 0.06 ppb | California public health goal | Lung cancer; breast cancer; colon cancer; harm to the kidney; harm to the liver; harm to the central nervous system |
| Thallium | 2 ppb | 0.1 ppb | California public health goal |
Hair loss; harm to the liver; harm to the central nervous system; harm to the brain and nervous system; harm to the male reproductive system |
| Toluene | 1 ppm | 0.15 ppm | California public health goal | Harm to the brain and nervous system; harm to the liver; harm to the immune system; harm to the reproductive system; harm to fetal growth and development |
| Total trihalomethanes (TTHMs) | 80 ppb | 0.15 ppb | EWG-recommended health guideline | Bladder cancer; skin cancer; harm to fetal growth and development |
| Toxaphene | 3 ppb | 0.03 ppb | California public health goal | Cancer; harm to the brain and nervous system; harm to the liver; harm to the kidney; hormone disruption |
| Tribromoacetic acid | Nonexistent | 0.04 ppb | EWG-recommended health guideline | Change to fetal growth and development |
| Trichloroacetic acid | Nonexistent | 0.1 ppb | California public health goal | Cancer; harm to reproduction and child development |
| Trichloroethylene | 5 ppb | 0.4 ppb | A risk assessment advisory level defined by the Minnesota Department of Health | Cancer; change to fetal growth and development; harm to the liver; harm to the kidney |
| Trichlorofluoromethane | Nonexistent | 1.3 ppm | California public health goal | Harm to the liver; change to the central nervous system; harm to the heart and blood vessels |
| Trichlorotrifluoroethane | Nonexistent | 4 ppm | California public health goal | Harm to the liver; change to the central nervous system; harm to the heart and blood vessels |
| Tritium | Nonexistent | 400 pCi/L | California public health goal | Cancer |
| Uranium | 30 ppb*** | 0.43 pCi/L | California public health goal | Cancer; harm to the kidney |
| Vanadium | Nonexistent | 21 ppb | Health benchmark defined by the Environmental Protection Agency for testing under the Unregulated Contaminant Monitoring Rule program | Change in blood chemistry; harm to reproduction and child development |
| Vinyl chloride | 2 ppb | 0.05 ppb | California public health goal | Liver cancer; harm to the liver; change to the central nervous system |
| Xylenes (total) | 10 ppm | 1.8 ppm | California public health goal | Harm to the brain and nervous system; change to the central nervous system; change to fetal growth and development |
* In 2024, the EPA set a Hazard Index MCL of 1 for mixtures containing two or more of PFHxS, PFNA, HFPO-DA, and PFBS to account for co-occurring levels of these PFAS in drinking water.
** In 2024, the EPA released the final Lead and Copper Rule Improvements which included lowering the lead action level from 15 to 10 ppb. It will go into effect November 2027.
** The legal limit for uranium is 30 micrograms per liter (corresponding to ppb), but the human health guideline for uranium is based on the overall radioactivity of the substance. Using an EPA conversion factor described in the 2002 EPA Implementation Guidance for Radionuclides, uranium test results can be converted from ppb to pCi/L. A measurement of 30 ppb is calculated to have a radioactivity level of 20 pCi/L.
February 2025