What is Dichloroacetic acid* and Why Does It Matter?

Dichloroacetic Acid: What It Is and Why It Matters

Dichloroacetic acid (DCA) is a disinfection byproduct — a chemical that forms when chlorine or chloramine reacts with natural organic matter in water. Think of it this way: utilities add chlorine to kill bacteria and viruses, which is essential. But when that chlorine meets decaying leaves, algae, or soil runoff, a chemical reaction produces compounds like DCA. It's an unintended consequence of keeping water free from pathogens. Older water systems, surface water sources, and areas with high organic content in the watershed tend to produce the most DCA.

The health concerns around dichloroacetic acid are serious enough to warrant attention. The International Agency for Research on Cancer (IARC) classifies DCA as a possible human carcinogen. Animal studies have linked it to liver tumors, and research suggests it may also affect the nervous system and reproductive health with long-term exposure (EWG). Even at low levels, DCA accumulates in the body over time. Children and pregnant women face the greatest risk because their bodies are more vulnerable to chemical disruption during development.

Here's where the numbers get concerning. The EPA's legal limit for the group of haloacetic acids (HAAs) — which includes DCA — is 60 parts per billion (ppb). That standard was set in 1998 and hasn't been updated since. The EWG's health guideline for dichloroacetic acid specifically is just 0.4 ppb, based on current cancer risk research. Across 565 water systems in the U.S., the average detected level of DCA is 6.797 ppb — that's nearly 17 times above the EWG health guideline. The highest recorded level hit 30.5 ppb. A staggering 539 of those 565 systems — more than 95% — exceeded the EWG guideline. Utilities aren't breaking the law, but that doesn't mean the water is without risk.

Certain states show up repeatedly in the data. New York leads with 54 affected systems, followed by Illinois (52), Massachusetts (42), Colorado (40), and California (38). This pattern isn't random. States with older infrastructure and surface water supplies — like rivers and reservoirs — tend to have higher DCA levels. Surface water picks up more organic material than groundwater, giving chlorine more to react with. Dense urban areas also tend to rely on heavily treated surface water, which increases byproduct formation. Seasonal spikes are common too, especially in late summer and fall when algae blooms and decaying organic matter peak in reservoirs.

The good news is that effective filtration options exist. Activated carbon filters can reduce DCA levels, but reverse osmosis (RO) is the most reliable method for removing disinfection byproducts from drinking water. A quality reverse osmosis system removes up to 99% of haloacetic acids, including dichloroacetic acid. Echo Water's reverse osmosis systems are designed specifically to address contaminants like DCA that fall through the gaps of outdated federal standards. Installing a point-of-use filter — meaning one connected directly to your kitchen tap or refrigerator — is the most practical step for most households. If you're in New York, Illinois, Massachusetts, Colorado, or California, it's worth pulling your annual water quality report (called a Consumer Confidence Report) to see exactly what your utility detected last year. You can find it on your utility's website or at EWG's Tap Water Database. Knowing your numbers is the first step toward protecting your family.

Regulatory Standards for Dichloroacetic acid*

Cities With the Highest Dichloroacetic acid* Levels

States Most Affected by Dichloroacetic acid*

Frequently Asked Questions

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