cis-1,2-Dichloroethylene in Drinking Water: Complete Guide (2026)

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

# cis-1,2-Dichloroethylene: What You Need to Know

## What It Is and Where It Comes From

cis-1,2-Dichloroethylene (often shortened to cis-DCE) is a volatile organic compound used primarily in industrial manufacturing. It's a colorless liquid with a sharp, sweet smell that evaporates easily into air and water. Most cis-DCE enters groundwater through industrial discharge, improper waste disposal, and contamination from dry cleaning facilities and metal degreasing operations. Once in the water supply, it persists because it breaks down very slowly in the environment. The compound also forms as a byproduct when other chlorinated solvents degrade in soil and groundwater, meaning contamination can spread even from old dumpsites and abandoned industrial sites.

## Health Effects and Exposure Risks

The EPA classifies cis-1,2-dichloroethylene as a possible human carcinogen based on animal studies. Exposure to high levels has been linked to liver and kidney damage in laboratory animals. The EPA's maximum contaminant level (MCL) is set at 70 parts per billion (ppb), a threshold designed to prevent serious health effects over a lifetime of drinking water exposure. However, the Environmental Working Group (EWG) recommends a stricter health guideline of 0.35 ppb based on cancer risk assessment. This significant difference matters: while 284 water systems detected cis-DCE, none currently exceed the EPA's legal limit, but many exceed the EWG's more protective standard. For pregnant women and young children, whose developing organs are more vulnerable, even lower exposures warrant concern.

## The Regulatory Gap

The EPA's current MCL of 70 ppb was established in 1994 and hasn't been updated since. The EWG's 0.35 ppb guideline reflects more recent toxicology research and assumes greater cancer risk than the EPA's original calculations. This gap between the two standards is important: your tap water can be legally compliant under EPA rules while still containing levels the EWG considers unsafe for long-term consumption. The average cis-DCE concentration detected across affected systems is 0.681 ppb, nearly twice the EWG guideline, though the maximum recorded level of 26.4 ppb remains below the EPA limit. As water quality science evolves, regulatory standards often lag behind health recommendations, which is why many health-conscious families choose to filter their water beyond what the law requires.

## Where It's Most Common

cis-1,2-Dichloroethylene shows a clear geographic pattern tied to industrial history. Iowa leads with 44 affected water systems, followed by Ohio (26), New York (25), California (19), and Wisconsin (17). These states share common characteristics: older industrial infrastructure, a legacy of manufacturing and chemical processing, and groundwater-dependent drinking water supplies. The Midwest's reliance on groundwater makes it particularly vulnerable because once contamination reaches underground aquifers, it can persist for decades. California's presence on the list reflects contamination from aerospace manufacturing and electronics production in populated areas. New York and Ohio show the impact of historical dry cleaning operations and metal fabrication industries concentrated in urban regions.

## Removing cis-DCE From Your Water

Activated carbon filters are highly effective at removing cis-1,2-dichloroethylene from drinking water. Both granular activated carbon (GAC) and solid block carbon filters can reduce cis-DCE concentrations by 85-95% under proper conditions. Reverse osmosis systems provide even better removal, typically eliminating 95-99% of the compound. If you live in Iowa, Ohio, New York, or other affected regions and your water system has detected cis-DCE, a point-of-use filter on your kitchen tap or a whole-home carbon system offers practical protection. Have your water tested first to know your baseline level—this helps you choose the right filtration strength and verify that your system is working effectively. Echo Water's testing services can identify whether cis-DCE is present in your home's water supply, and our carbon filtration systems are specifically designed to handle volatile organic compounds like this one.

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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