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

1,1-Dichloroethylene (also called 1,1-DCE or vinylidene chloride) is a colorless, flammable liquid chemical used primarily in industrial manufacturing. It's most commonly produced as a byproduct of making plastics, adhesives, and food packaging materials. When industrial facilities improperly dispose of solvents or experience chemical spills, 1,1-DCE can seep into groundwater and eventually reach drinking water supplies. It also forms when other chlorinated solvents — like trichloroethylene — break down underground over time. That means even old contamination sites can continue releasing this chemical into water sources for decades.

The health concerns around 1,1-DCE are real, though the risk depends heavily on how much you're exposed to and for how long. Short-term exposure at high levels can affect the liver and central nervous system, causing symptoms like dizziness and nausea. Long-term exposure is more worrying. Animal studies have linked 1,1-DCE to liver and kidney damage, and the EPA classifies it as a possible human carcinogen (cancer-causing agent). The International Agency for Research on Cancer (IARC) has also flagged it for concern. Children and pregnant women face the greatest risk, since developing bodies are more sensitive to chemical exposure at any level.

The EPA's current legal limit — called the Maximum Contaminant Level (MCL) — for 1,1-DCE in drinking water is 7 parts per billion (ppb). The good news is that all 33 water systems where 1,1-DCE was detected are currently operating below that legal threshold. The average detected level across those systems was just 0.065 ppb, with the highest recorded sample reaching 0.25 ppb. That's well under the EPA limit. However, it's worth knowing that legal limits aren't always the same as safe limits. The EPA's standards are set by balancing health risk against what's technically and economically feasible to remove — not purely on what's safest for long-term health.

Geographically, California accounts for the largest share of detections, with 16 of the 33 affected water systems located there. Alabama follows with 5 systems, Wisconsin with 4, New York with 3, and Idaho with 2. California's high count isn't surprising — the state has a long industrial history, a large number of Superfund cleanup sites, and extensive groundwater monitoring programs that catch contaminants other states might miss. Alabama and Wisconsin both have significant manufacturing and industrial histories, which increases the likelihood of solvent contamination in nearby groundwater. States with more aggressive water testing programs tend to report more detections, not necessarily because their water is worse, but because they're looking more carefully.

The most effective way to remove 1,1-DCE from drinking water is through activated carbon filtration or reverse osmosis (RO). Activated carbon filters work by trapping chemical compounds as water passes through. Reverse osmosis goes further — it pushes water through a semi-permeable membrane that blocks up to 99% of dissolved contaminants, including 1,1-DCE. If you're on a municipal water supply that has detected this chemical, an under-sink reverse osmosis system is the most reliable option for your drinking and cooking water. Echo Water's reverse osmosis systems are designed specifically to address contaminants like 1,1-DCE, giving you an extra layer of protection beyond what your water utility provides. Whole-house carbon filtration can also reduce exposure at every tap, which matters for showering and bathing, since some chlorinated solvents can be absorbed through skin or inhaled as steam. If you're unsure what's in your local water, starting with a certified water quality test is the smartest first step — it tells you exactly what you're dealing with before you invest in any filtration system.

Regulatory Standards for 1,1-Dichloroethylene*

Cities With the Highest 1,1-Dichloroethylene* Levels

States Most Affected by 1,1-Dichloroethylene*

Frequently Asked Questions

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