Summary
Many tap water contaminants can transfer from water into air and can enter the body through the skin during or after a shower or bath. The federal government classifies such substances as volatile organic compounds, or VOCs.
These pollutants come from multiple sources, including gasoline, solvents, paints, cars, carpets and shower curtains. They can enter drinking water supplies from industrial sites and landfills, and from improper disposal at homes and businesses.
Between 1987 and 1992, the Environmental Protection Agency set legal limits for 21 different VOCs in tap water. But the limits allow much greater exposure to VOCs than what many public health agencies say is needed to minimize threats to human health. Since 1992, the EPA has not updated its existing standards for VOCs in drinking water or issued any new limits.
In other words, more legal limits for VOCs are needed, and the ones that have already been set must be updated to better protect people.
The full range of potential VOC contaminants in everyday environments may include hundreds of chemicals. Most worrisome are those that harm the developing fetus or increase the risk of cancer.
This report highlights 12 carcinogenic VOCs EWG believes should be regulated as a group of tap water contaminants.
Carcinogenic VOCs in tap water
In 2011, the EPA recommended establishing a single drinking water standard for a group of
carcinogenic VOCs, but has not yet proposed it. Of the 12 VOCs listed in the table below, the EPA
recommended including nine in a group of potentially carcinogenic VOCs.
EWG believes three additional chemicals should be added to the list: 1,4-dioxane, styrene and
1,1,2-trichloroethane.
| Carcinogenic VOC* | Federal legal limit, in ppb | Level posing one-in-a-million cancer risk1 | Reference | Classification2 |
|---|---|---|---|---|
| 1,2,3-Trichloropropane | N/A | 0.0007 | California public health goal | Likely to be carcinogenic to humans |
| Vinyl chloride | 2 | 0.05 | California public health goal | Known human carcinogen |
| Tetrachloroethylene (PCE or PERC) | 5 | 0.06 | California public health goal | Likely to be carcinogenic to humans |
| Carbon tetrachloride | 5 | 0.1 | California public health goal | Likely to be carcinogenic to humans |
| Benzene | 5 | 0.15 | California public health goal | Known human carcinogen |
| 1,1,2-Trichloroethane | 5 | 0.3 | California public health goal | Possible human carcinogen |
| 1,4-Dioxane | N/A | 0.35 | EPA one-in-a-million cancer risk level | Likely to be carcinogenic to humans |
| 1,2-Dichloroethane | 5 | 0.4 | California public health goal | Probable human carcinogen |
| Styrene | 100 | 0.5 | California public health goal | Reasonably anticipated to be a human carcinogen |
| 1,2-Dichloropropane | 5 | 0.5 | California public health goal | Carcinogenic to humans |
| Trichloroethylene (TCE) | 5 | 0.5 | EPA one-in-one-million cancer risk level | Carcinogenic to humans |
| Dichloromethane (methylene chloride) | 5 | 4 | California public health goal | Likely to be carcinogenic to humans |
* Click on a contaminant above to see its nationwide testing results.
1. Concentration that corresponds to a one-in-one-million cancer risk as defined by the California Office of Environmental Health Hazard Assessment and the EPA Integrated Risk Information System, or IRIS.
2. Carcinogenicity classifications come from the EPA IRIS program, except for two contaminants, styrene and 1,2-dichloropropane, which have not been assessed by IRIS for carcinogenicity. In 2011, the National Toxicology Program classified styrene as “reasonably anticipated to be a human carcinogen.” In 2016, the International Agency for Research on Cancer classified 1,2-dichloropropane as “carcinogenic to humans.”
What are the health effects of exposure to VOCs?
VOCs are linked to various types of cancer. For instance:
- Benzene increases the risk of leukemia and lymphoma.
- Carbon tetrachloride, a solvent, increases the risk of non-Hodgkin lymphoma.
- Tetrachloroethylene, or PERC, a dry-cleaning chemical, can cause bladder cancer.
- Trichloroethylene, or TCE, a solvent and dry-cleaning chemical, can cause liver, kidney and blood cancer.
Some VOCs are not known to cause cancer but can cause other serious health problems. For example, toluene, ethylbenzene and xylene are toxic to the liver, kidneys and nervous system. Toluene is reported to harm the function of hormones.
How do VOCs get in water?
VOCs are used in a wide variety of industrial and commercial products and processes. Disposal at municipal and industrial landfills across the country, as well as commercial and residential applications, have contributed to VOC contamination of drinking water supplies.
A 2006 U.S. Geological Survey study of groundwater and drinking water wells found VOCs in 90 of 98 aquifers tested nationwide, with the most frequent detections in California, Florida, Nevada and the New England and mid-Atlantic states. Some groundwater samples were contaminated with more than one VOC.
Is there a safe level of VOCs in water?
For most individual VOCs, limits that pose the one-in-a-million cancer risk defined by California’s public health goals or the EPA are adequate. But to protect children, the levels of some VOCs, such as trichloroethylene, need to be more strict.
Even these benchmarks may fall short, because people are exposed to VOCs and other pollutants simultaneously. That’s why EWG urges federal and state health agencies to regulate carcinogenic VOCs as a group.
What can you do to reduce your exposure to VOCs in drinking water?
There are many sources of VOC exposure:
- Drinking tap water that comes from polluted sources that have not been properly treated to remove VOCs.
- Inhaling VOCs that got into indoor air from contaminated tap water.
- Bathing or showering in water that carries VOCs.
- Inhaling indoor and outdoor air with VOCs that emanate from consumer products, or from industrial and commercial facilities that use these chemicals.
How can VOCs be reduced in drinking water?
Here’s a quick summary of water treatment for VOCs:
- Many VOCs, though not all, can be effectively removed or minimized with basic countertop activated carbon filters, an economical option for mitigating water quality problems.
- More expensive technologies, such as reverse osmosis, offer even better water purification. This type of filter can be installed at the tap or as a whole-house water treatment.
- Certain VOCs, such as 1,4-dioxane, can’t be effectively removed by in-home water filtration systems. These can be removed fully only at the water utility level, because they require specialized treatment. For example, reverse osmosis only partially removes 1,4-dioxane.
Shoppers can use EWG’s water filter guide to find a product that will remove specific water contaminants, including many VOCs.
For people who rely on drinking water from private wells, EWG recommends regular water testing, in line with guidance from federal and state public health agencies. This testing is especially important for VOCs for private well owners in areas where there may be underground fuel storage tanks, or those near gas stations, dry-cleaning facilities and landfills.
References
Environmental Protection Agency, Integrated Risk Information System Assessment for 1,2-Dichloroethane. 1987. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=149
California Office of Environmental Health Hazard Assessment, Public Health Goal for 1,2-Dichloropropane in Drinking Water. 1999. Available at https://oehha.ca.gov/media/downloads/water/public-health-goal/12dcpf.pdf
Environmental Protection Agency, Integrated Risk Information System Assessment for 1,1,2-Trichloroethane. 1987. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=198
EPA, Integrated Risk Information System Assessment for Benzene. 2000. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=276
EPA, Integrated Risk Information System Assessment for Vinyl Chloride. 2000. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=1001
EPA, Integrated Risk Information System Assessment for 1,2,3-Trichloropropane. 2009. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=200
EPA, Integrated Risk Information System Assessment for Carbon Tetrachloride. 2010. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=20
EPA,. Basic Questions and Answers for the Drinking Water Strategy Contaminant Groups Effort. EPA 815-F-11-002, 2011. Available at nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100NRW9.TXT
EPA, Integrated Risk Information System Assessment for Dichloromethane. 2011. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=70
EPA, Integrated Risk Information System Assessment for Trichloroethylene. 2011. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=199
EPA, Integrated Risk Information System Assessment for Tetrachloroethylene. 2012. Available at cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=106
EPA, Integrated Risk Information System Assessment for 1,4-Dioxane. 2013. Available at cfpub.epa.gov/ncea/iris2/chemicallanding.cfm?substance_nmbr=326
EPA, Volatile Organic Compounds’ Impact on Indoor Air Quality. 2016. Available at epa.gov/indoor-air-quality-iaq/volatile-organic-compounds-impact-indoor-air-quality
International Agency for Research on Cancer, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 71. Re-Evaluation of Some Organic Chemicals, Hydrazine and Hydrogen Peroxide. 1999. Available at monographs.iarc.fr/ENG/Monographs/vol71/index.php
International Agency for Research on Cancer, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 82. Some Traditional Herbal Medicines, Some Mycotoxins, Naphthalene and Styrene. 2002. Available at monographs.iarc.fr/ENG/Monographs/vol82/index.php
International Agency for Research on Cancer, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100F. Chemical Agents and Related Occupations. 2012. Available at monographs.iarc.fr/ENG/Monographs/vol106/index.php
International Agency for Research on Cancer, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 106. Trichloroethylene, Tetrachloroethylene and Some Other Chlorinated Agents. 2014. Available at monographs.iarc.fr/ENG/Monographs/vol106/index.php
International Agency for Research on Cancer, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 110. Some Chemicals Used as Solvents and in Polymer Manufacture. 1,2-Dichloropropane. 2016. Available at monographs.iarc.fr/ENG/Monographs/vol110/mono110-03.pdf
National Toxicology Program, Report on Carcinogens: Styrene. 2011. Available at ntp.niehs.nih.gov/ntp/roc/content/profiles/styrene.pdf
P.J. Squillace et al. VOCs, Pesticides, Nitrate, and their Mixtures in Groundwater Used for Drinking Water in the United States. Environmental Science and Technology, 2002, 36(9):1923–1930
U.S. Geological Survey, The Quality of Our Nation’s Waters. Volatile Organic Compounds in the Nation’s Ground Water and Drinking-Water Supply Wells. 2006. Available at pubs.usgs.gov/circ/circ1292
Water Research Foundation, Background Technical Information for Carcinogenic Volatile Organic Compounds (cVOCs). 2015. Available at https://www.waterrf.org/news/carcinogenic-vocs-contaminant-group-filling-critical-knowledge-gaps-inform-meaningful
February 2025