1,4-Dioxane in Tap Water: Sources, Cancer Risk, and Why There's No Federal Limit

1,4-dioxane is an industrial chemical that shows up in groundwater near old solvent spills and in some wastewater-affected rivers. EPA classifies it as “likely to be carcinogenic to humans,” based mainly on liver and nasal tumors in animal studies. There is no enforceable federal drinking water limit, and in March 2026 EPA again declined to make a regulatory decision on it. New York became the first state to enforce a limit, 1 µg/L (1 part per billion), in 2020. California uses a 1 µg/L notification level. Boiling doesn’t remove it, water utilities typically rely on advanced oxidation, and as of the most recent state guidance we found, no home filter is certified to remove it.

What 1,4-dioxane is and where it comes from

1,4-dioxane is a clear liquid that mixes completely with water. According to EPA’s technical fact sheet and its chemical risk evaluation, it has been used or produced:

As a stabilizer for chlorinated solvents, especially 1,1,1-trichloroethane (TCA). EPA notes 1,4-dioxane is frequently found at sites contaminated with TCA.
As an industrial solvent and processing aid, and in adhesives, sealants, inks and lubricants
As a byproduct in manufacturing, including in the making of PET plastic
As a contaminant in consumer products, including some detergents, cleaning products, shampoos and cosmetics, where it forms as an unintended byproduct

Two properties make it a groundwater problem. EPA says it moves quickly from soil into groundwater and can travel ahead of other contaminants in a plume. It is also relatively resistant to breaking down in soil and water. As of 2016, EPA had identified it at more than 34 Superfund (National Priorities List) sites.

It can also reach rivers through wastewater. California’s water board notes that some wastewater treatment plants are required to monitor it in their discharges and the waterways that receive them.

Health effects

The main concern is cancer from long-term exposure.

EPA’s IRIS program (2013) classifies 1,4-dioxane as “likely to be carcinogenic to humans” by all routes of exposure.
The U.S. Department of Health and Human Services says it is “reasonably anticipated to be a human carcinogen,” based on animal studies.
Animal studies showed increased liver, nasal cavity and gallbladder tumors. EPA’s non-cancer reference dose is based on liver and kidney effects in animals.
Short-term exposure to high levels (mostly a workplace issue) can cause nausea, drowsiness, headache and eye, nose and throat irritation.

EPA estimates that drinking water with 0.35 µg/L over a lifetime corresponds to a one-in-a-million added cancer risk. That number is a risk benchmark, not a legal limit. California, for example, set its notification level at 1 µg/L partly because labs had trouble measuring lower levels when it was adopted.

Health agencies don’t agree on how potent it is. Health Canada’s drinking water guideline, finalized in March 2021, is 50 µg/L, far higher than the US risk benchmarks. And EPA’s chemicals office is currently reconsidering the cancer analysis behind its TSCA risk evaluation (more below).

Why there’s no federal limit

1,4-dioxane has been on EPA’s radar for more than a decade, without a regulation:

2013 to 2015: Large public water systems tested for it under EPA’s third Unregulated Contaminant Monitoring Rule (UCMR 3).
CCL 5 (2022): It is on EPA’s fifth Contaminant Candidate List, the list of unregulated contaminants under study.
March 2026: In its final Regulatory Determination 5, EPA made no preliminary determination for 1,4-dioxane. EPA said its occurrence in UCMR 3 at levels relevant to its health benchmarks (0.35 and 35 µg/L) was “limited,” and that it would keep evaluating health and occurrence data. It noted it may evaluate 1,4-dioxane again in a future round of UCMR monitoring.

Separately, under the Toxic Substances Control Act (TSCA), EPA finalized a risk evaluation in December 2020 and a supplement in November 2024 that looked at exposure through drinking water and air. In its March 2026 response to comments, EPA said it is administratively reconsidering the 2024 supplement and revised risk determination, along with the 2020 evaluation, focusing on the cancer risk analysis. Results may inform future agency action.

Bottom line on status (October 2026): No federal drinking water limit exists, none has been proposed, and EPA’s underlying cancer assessment for TSCA purposes is under review. We could not confirm any federal action beyond that.

State limits and guidelines

New York set the first enforceable state limit (MCL) in the country in 2020: 1 µg/L. It came from a 2018 recommendation by the state’s Drinking Water Quality Council and was adopted alongside limits of 10 parts per trillion for PFOA and PFOS. New York public water systems must monitor for 1,4-dioxane on a regular schedule. Find New York utilities on our New York page.

California has a notification level of 1 µg/L, set in November 2010 after EPA updated its cancer estimate, and a response level of 35 µg/L, at which the state recommends taking a source out of service. Notification levels are advisory, not enforceable, and the state says water systems are not required by state regulation to monitor for 1,4-dioxane. In September 2025, California’s Office of Environmental Health Hazard Assessment released a draft public health goal of 0.04 µg/L, a step toward a possible future enforceable limit. See California public health goals explained for how that process works.

Many other states have non-enforceable guidance values for groundwater or drinking water. EPA’s 2017 fact sheet listed values from 0.25 µg/L to 77 µg/L, so the guidance varies widely.

How to find out if it’s in your water

Check your water quality report. In New York, 1,4-dioxane is a regulated contaminant, so detections should appear with the other regulated results. Elsewhere, it may appear under unregulated contaminants if your system has tested for it. Our guide to reading your water quality report shows where to look.
Ask your utility whether it has tested, especially if you live near a former industrial or solvent-contaminated site.
Look up your utility through our ZIP code search. Results for 1,4-dioxane are only available where systems have tested and reported them.
Private wells near known solvent contamination should be tested by a certified lab using a method that can detect low levels. EPA developed Method 522 for drinking water.

Treatment: what works and what doesn’t

1,4-dioxane is hard to remove. EPA notes it is hydrophilic (it prefers to stay dissolved in water), so treatment has to be tailored to its unusual properties.

At treatment plants: Advanced oxidation processes (AOP) are the main tool. They use ultraviolet light with hydrogen peroxide, or ozone with peroxide, to create highly reactive molecules that break 1,4-dioxane apart. California’s water board says AOP using peroxide with UV or ozone has been shown to destroy 1,4-dioxane, and California requires certain recycled water projects to demonstrate AOP removal of it.

At home:

No certified home devices. California’s water board says there are currently no standards for home treatment devices that specifically include 1,4-dioxane, and its device program doesn’t register any certified to remove it. New Jersey’s Department of Environmental Protection says no home devices have been certified for 1,4-dioxane removal by NSF or UL.
Partial help only. California says reverse osmosis and granular activated carbon filters registered for VOC reduction “may be moderately effective,” and that devices vary greatly in performance. A VOC claim is not a 1,4-dioxane claim. See reverse osmosis vs. carbon filters for how these technologies differ.
Boiling doesn’t remove it, according to New Jersey’s Department of Environmental Protection.
Bottled water is an option, but California notes that bottled water makers aren’t required to test for or remove 1,4-dioxane.

Because the certification picture can change, check the NSF and other accredited certifier listings for a specific 1,4-dioxane claim before relying on any product.

Bottom line

1,4-dioxane is a likely carcinogen that moves easily through groundwater and is hard to treat. There’s no federal limit, and EPA chose in March 2026 to keep studying it rather than decide. New York enforces 1 µg/L, California advises at 1 µg/L and has proposed a much lower health goal, and Health Canada uses 50 µg/L. If you live near solvent contamination or in an affected area, ask your utility for its results, test a private well, and know that home filters are not certified for this chemical.