What is 1,1-Dichloroethane* and Why Does It Matter?

1,1-Dichloroethane (also called 1,1-DCA) is a synthetic chemical that doesn't occur naturally in the environment. It's a byproduct of industrial processes — most commonly linked to chemical manufacturing, dry cleaning operations, and the production of other chlorinated solvents. It enters drinking water primarily through contaminated groundwater. When factories improperly dispose of chemical waste, or when underground storage tanks leak, 1,1-DCA can seep into the soil and eventually reach the water supply. It's also sometimes found as a breakdown product of other chlorinated compounds, which means it can show up even at sites where it was never directly used.

The health picture for 1,1-DCA is still developing, but the available evidence raises legitimate concerns. Animal studies show that prolonged exposure can damage the liver and kidneys. The International Agency for Research on Cancer (IARC) has classified it as a possible human carcinogen, meaning there's enough evidence to take it seriously, even if the full picture isn't complete. Short-term exposure at very high levels can cause dizziness, nausea, and central nervous system effects. At the low levels found in drinking water — the average detected across U.S. systems is just 0.03 parts per billion (ppb) — the immediate risk is minimal. But long-term, low-level exposure is exactly the kind of scenario where precaution makes sense, especially for children and pregnant women.

Right now, the EPA has not set a Maximum Contaminant Level (MCL) specifically for 1,1-DCA in drinking water. That means there's no federal legal limit that water utilities must stay under. The EPA does maintain a health advisory, but the absence of a hard regulatory limit means utilities aren't required to take action even when it's detected. The Environmental Working Group (EWG) tracks this contaminant closely and notes that current detection levels across the country remain below existing health advisory thresholds — which is reflected in the data: of the 144 water systems that detected 1,1-DCA, zero reported levels above the guideline. Still, "below the guideline" doesn't always mean "no risk." It means the levels are within what regulators currently consider acceptable, not that the chemical is harmless.

Geographically, 1,1-DCA shows up most often in states with heavy industrial histories. California leads with 25 water systems detecting it, followed closely by New Jersey with 23. Illinois, New York, and Vermont round out the top five, with 11, 10, and 8 systems respectively. California and New Jersey make sense given their dense concentrations of manufacturing sites and Superfund cleanup locations. Vermont's presence on this list is more surprising — it likely reflects contamination from older industrial or dry-cleaning sites in smaller communities where groundwater is the primary drinking water source. The highest single detection recorded was 0.307 ppb, well above the 0.03 ppb average, which tells us that while most detections are low, localized hotspots do exist.

The good news is that 1,1-DCA is very treatable with the right filtration technology. Activated carbon filtration — the kind found in many under-sink and countertop filters — can reduce 1,1-DCA levels significantly. For the most thorough protection, reverse osmosis (RO) systems are the gold standard. A quality RO system removes up to 99% of chlorinated volatile organic compounds (VOCs) like 1,1-DCA from your drinking water. If you're in California, New Jersey, or another high-detection state and your water comes from a groundwater source, it's worth knowing what's in your water before assuming it's clean. Echo Water's systems use multi-stage filtration that includes both activated carbon and reverse osmosis, designed specifically to address contaminants like 1,1-DCA that fall through regulatory gaps. The first step is always testing — understanding what's actually coming out of your tap gives you the information you need to make a smart decision for your family.

Regulatory Standards for 1,1-Dichloroethane*

Cities With the Highest 1,1-Dichloroethane* Levels

States Most Affected by 1,1-Dichloroethane*

Frequently Asked Questions

Related Contaminant Guides