1,4-Dioxane in Drinking Water

At a Glance

What Is 1,4-Dioxane?

According to the federal Agency for Toxic Substances and Disease Registry (ATSDR), “1,4-Dioxane is a clear liquid that easily dissolves in water.”⁠^[4] ATSDR explains that “It is used primarily as a solvent in the manufacture of chemicals and as a laboratory reagent.”⁠^[4]

It can also turn up in everyday products. In ATSDR’s words, “1,4-Dioxane is a trace contaminant of some chemicals used in cosmetics, detergents, and shampoos.”⁠^[4]

Why It Matters for Groundwater

Two of its properties matter for groundwater. ATSDR notes that “In water, 1,4-dioxane is stable and does not break down,” and that “In soil, 1,4-dioxane does not stick to soil particles, so it can move from soil into groundwater.”⁠^[4]

Groundwater is especially important on Long Island. The U.S. Geological Survey states that “Groundwater is the sole source of freshwater supply in Nassau and Suffolk Counties on Long Island.”⁠^[6] When New York’s Department of Environmental Conservation (DEC) finalized its rules for consumer products in 2024, it reported:

“1,4-dioxane has been found in groundwater at sites throughout the U.S., particularly in Long Island’s sole source aquifer and in association with legacy industrial and hazardous waste sites.”

DEC also points to “the need for complex and costly treatment technologies to remove it from drinking water supplies.”⁠^[5]

Drinking Water Limits

EPA defines a maximum contaminant level (MCL) as “The highest level of a contaminant that is allowed in drinking water.”⁠^[7] New York set one for 1,4-dioxane before any other state. In the words of the New York State Department of Health:

“In 2020, New York State set MCLs of 10 parts per trillion (10 ppt) for PFOA and PFOS, and 1 part per billion (1 ppb) for 1,4-dioxane. New York was the first state to develop an MCL for 1,4-dioxane.”

The Department of Health adds that “Public water systems in New York must monitor for more than 100 different contaminants on a regular schedule, including PFOA, PFOS and 1,4-dioxane.”⁠^[1]

At the federal level, there is no national drinking water regulation for 1,4-dioxane. It appears on EPA’s fifth Contaminant Candidate List (CCL 5),⁠^[2] which EPA describes as “a list of contaminants that are currently not subject to any proposed or promulgated national primary drinking water regulations but are known or anticipated to occur in public water systems.”⁠^[3]

Limits on Household Products

New York also limits how much 1,4-dioxane some everyday products may contain. Since December 31, 2023, the limit for household cleansing and personal care products has been 1 part per million (ppm), and since December 31, 2022, the limit for cosmetics has been 10 ppm.⁠^[5,8]

DEC says “New York is the first state in the nation to adopt regulations that reduce 1,4-dioxane in these product categories to help protect consumers and natural resources and create healthier communities.”⁠^[5] Temporary waivers for manufacturers ended on December 30, 2025, after which “all products will need to comply with the limits.”⁠^[8]

How to Check Your Water

If your home is on public water

Your water supplier publishes an annual drinking water quality report. EPA says “Reports must be sent by your water supplier each year by July 1,” and each report includes “The regulated contaminant found in local drinking water.”⁠^[9] The New York State Department of Health also lets you “Find and map a large public water system closest to you and view its Annual Drinking Water Quality Report.”⁠^[10]

If you have a private well

EPA notes that “Private well owners are responsible for delivering safe drinking water to their households.”⁠^[11] In Suffolk County, the Department of Health Services “operates an extensive water testing program” to help residents with private wells.⁠^[12] Our private well guide covers testing in more detail.