What is cis-1,2-Dichloroethylene* and Why Does It Matter?

Cis-1,2-Dichloroethylene (also written as cis-1,2-DCE) is a colorless, flammable liquid that evaporates easily and dissolves in water. It doesn't usually start in your water supply on its own. Instead, it forms underground when other industrial solvents — particularly trichloroethylene (TCE) and tetrachloroethylene (PCE) — break down in soil and groundwater. These parent chemicals were widely used in dry cleaning, metal degreasing, and manufacturing for decades. As they slowly degrade, cis-1,2-DCE is one of the byproducts left behind. That means its presence often signals a longer history of industrial contamination nearby.

Right now, cis-1,2-DCE has been detected in 89 water systems across the United States. The average level measured is 0.408 parts per billion (ppb), with the highest recorded level reaching 2.98 ppb. Importantly, none of the 89 systems currently exceed the EPA's legal limit. That's reassuring on the surface, but it doesn't mean the risk is zero — especially with long-term, low-level exposure.

The health picture with cis-1,2-DCE is still developing, but animal studies raise legitimate concerns. High-dose exposure has been linked to liver and kidney damage in animal research. The EPA classifies cis-1,2-DCE as a possible human carcinogen, meaning there's enough evidence to warrant caution, even if the science isn't fully settled. The EPA's current Maximum Contaminant Level (MCL) — the legal limit utilities must meet — is set at 70 ppb. That number may sound reassuring given the levels detected, but the Environmental Working Group (EWG) and independent researchers argue that legal limits for chlorinated solvents like this one haven't kept pace with newer health research. When a contaminant forms as a breakdown product of known carcinogens like TCE, it deserves close attention at any level.

Geographically, the detections follow a clear industrial pattern. Iowa leads with 30 affected water systems, followed by Ohio with 13, and then New York, Illinois, and Wisconsin with 6, 6, and 5 systems respectively. This concentration in the Midwest and Great Lakes region isn't a coincidence. These states have deep histories of heavy manufacturing, agricultural chemical use, and industrial solvent disposal — activities that left contamination in the ground that's still working its way into water sources today. Many of these detections trace back to old industrial sites, former dry cleaners, or areas where solvent disposal was poorly regulated before the 1980s. If you live near a former industrial zone or a Superfund cleanup site in these states, your water deserves a closer look.

The good news is that cis-1,2-DCE is very treatable with the right filtration. Reverse osmosis (RO) is the most effective method, removing up to 99% of chlorinated volatile organic compounds (VOCs) like cis-1,2-DCE from drinking water. Activated carbon filtration — particularly granular activated carbon (GAC) — also performs well against this contaminant. A quality under-sink RO system, like the ones Echo Water offers, handles cis-1,2-DCE along with dozens of other contaminants in a single step. If you're on well water in Iowa, Ohio, or any of the other high-detection states, testing your water first is the smart move. Knowing your actual levels helps you choose the right solution rather than guessing. Even if your utility reports compliance with EPA limits, filtration at the tap gives you an added layer of protection — especially for children and pregnant women, who are more vulnerable to chemical exposures at lower doses.

Regulatory Standards for cis-1,2-Dichloroethylene*

Cities With the Highest cis-1,2-Dichloroethylene* Levels

States Most Affected by cis-1,2-Dichloroethylene*

Frequently Asked Questions

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