1,4-Dioxane, New York’s emerging-contaminant standards, and what they mean for Nassau and Suffolk homeowners
Long Island draws all of its drinking water from a single underground aquifer, which makes emerging contaminants like 1,4-dioxane a regional concern — and the reason New York set the nation’s first drinking-water limit for it.
What it is
What is 1,4-dioxane?
1,4-Dioxane is a synthetic industrial chemical historically used as a stabilizer in solvents and found as a byproduct in some detergents, shampoos, and cosmetics. The EPA classifies it as likely to be carcinogenic to humans. It dissolves easily in water, does not cling to soil, and is not removed by conventional carbon filtration or standard treatment — which is why it can travel through groundwater and reach drinking-water wells.
Why Long Island
Why is this a Long Island issue specifically?
Nassau and Suffolk counties sit over a federally designated sole-source aquifer — there is no reservoir or river backup, so all drinking water is pumped from groundwater. Decades of industrial activity, household product use, and the chemical’s mobility have left detectable 1,4-dioxane in parts of the aquifer. Long Island has among the highest reported 1,4-dioxane levels in the country, which is what pushed the issue to the front of New York’s drinking-water agenda.
The standard
New York’s 1 ppb maximum contaminant level
In 2020, New York became the first state to adopt an enforceable drinking-water standard (Maximum Contaminant Level, or MCL) for 1,4-dioxane, set at 1 part per billion (ppb). Public water systems that exceed it must treat the water or take the source offline. This standard, adopted alongside first-in-the-nation MCLs for PFOA and PFOS, is enforced by the New York State Department of Health.
Treatment
How districts remove it
Because carbon and reverse osmosis are only partially effective, the proven treatment for 1,4-dioxane is advanced oxidation process (AOP) — combining UV light with hydrogen peroxide to break the molecule apart. Long Island water providers (including the Suffolk County Water Authority and numerous Nassau districts such as Hicksville) have installed AOP systems at affected well fields, a significant regional infrastructure investment.
For homeowners
What can a homeowner do?
- Read your water district’s annual Consumer Confidence Report (CCR) — Long Island providers report 1,4-dioxane results.
- If you’re on a private well (less common on Long Island but present in some areas), consider testing through an ELAP-approved lab, since wells aren’t covered by a CCR.
- For point-of-use treatment, note that only specific certified systems address 1,4-dioxane; standard carbon pitchers do not.
- Reduce household sources by choosing products certified as 1,4-dioxane-free where possible.
FAQ
Frequently asked questions
Is Long Island tap water safe to drink given 1,4-dioxane?
Public water systems on Long Island must meet New York’s 1 ppb standard for 1,4-dioxane; where levels exceeded it, districts have installed advanced oxidation treatment or taken sources offline. Check your district’s current CCR for its reported results.
Does a regular carbon filter remove 1,4-dioxane?
No. 1,4-dioxane is not effectively removed by standard carbon filtration or by most home pitchers. Utilities use advanced oxidation (UV plus hydrogen peroxide); only specific certified point-of-use systems address it at home.
Where can I see my area’s 1,4-dioxane levels?
Your water provider’s annual Consumer Confidence Report lists it. Suffolk County Water Authority and Nassau water districts publish these, and SCWA offers an address-searchable report. See your county guide for links.
NY Water Quality Guide is an independent educational resource and is not affiliated with or endorsed by any government agency or utility. This page is general education, not legal, medical, or regulatory advice. Verify current standards and any health guidance with the NYS Department of Health and the EPA.
Last reviewed: July 2026