What is 1,2,3-Trichloropropane* and Why Does It Matter?

1,2,3-Trichloropropane (TCP) is a synthetic chemical that has no natural sources. It was never meant to end up in drinking water. For decades, chemical companies used TCP as a solvent and as a raw material to make other industrial chemicals. It also appeared as an unwanted byproduct in soil fumigants — pesticides used heavily in agriculture from the 1940s through the 1980s. When those fumigants were applied to fields, TCP seeped into the soil and eventually reached groundwater. Unlike many contaminants, TCP doesn't break down easily underground. It can persist in aquifers for decades, which is why water systems are still detecting it today, long after the original source was removed.

The health concerns around TCP are serious. The EPA and the International Agency for Research on Cancer (IARC) classify it as a probable human carcinogen, meaning it likely causes cancer based on animal studies and available evidence. Research shows TCP damages DNA and has caused tumors in multiple organs in animal testing. There is no known "safe" level of exposure — even very low concentrations carry some degree of risk over a lifetime of drinking. The EWG sets its health guideline at just 0.0000007 ppb, a number that reflects a one-in-a-million cancer risk over a lifetime of consumption. That's an extraordinarily cautious threshold, and it exists for good reason.

Here's where the regulatory gap becomes a real problem. The EPA has not set a legal limit — called a Maximum Contaminant Level (MCL) — for TCP in federal drinking water. That means water utilities can detect TCP in your tap water and still be in full legal compliance. California is one of the few states that has stepped in with its own standard, setting an MCL of 0.005 ppb. But even that state limit is far above the EWG health guideline. Across the 164 water systems where TCP has been detected nationally, 104 of them — nearly two-thirds — show levels that exceed the EWG guideline. The average detected level is 0.017 ppb, and the highest recorded level reaches 0.25 ppb. That's more than 350,000 times above the EWG's health benchmark.

Geographically, TCP contamination follows the footprint of industrial agriculture and chemical manufacturing. Texas leads the country with 70 affected water systems, followed by New Jersey at 35, California at 32, New York at 13, and Alabama at 6. Texas and California's numbers reflect decades of heavy agricultural fumigant use on large-scale farming operations. New Jersey's contamination connects more to its dense industrial history — the state has one of the highest concentrations of Superfund sites in the country, many of them linked to chemical production. In all of these states, the contamination tends to concentrate in communities that rely on groundwater wells rather than surface water sources like rivers or reservoirs.

The good news is that TCP is very effectively removed by the right filtration technology. Granular activated carbon (GAC) filters can reduce TCP levels, but the most reliable protection comes from reverse osmosis (RO) filtration. Reverse osmosis forces water through a semi-permeable membrane with pores small enough to block TCP molecules, removing up to 99% of the contaminant. An Echo Water reverse osmosis system installed at your kitchen sink gives you a practical, affordable layer of protection — especially if you live in Texas, New Jersey, California, or another high-risk state. If you're on a private well, testing your water first is an important step. Many homeowners don't realize their well water is unregulated at the federal level, meaning no one is monitoring it on your behalf. Knowing what's in your water is the first step. Filtering it out is the second.

Regulatory Standards for 1,2,3-Trichloropropane*

Cities With the Highest 1,2,3-Trichloropropane* Levels

States Most Affected by 1,2,3-Trichloropropane*

Frequently Asked Questions

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