What is DDT and Why Does It Matter?

DDT (dichlorodiphenyltrichloroethane) is one of the most well-known pesticides in history — and one of the most persistent. The U.S. banned DDT in 1972 after research linked it to widespread environmental damage, including the near-collapse of bald eagle populations. But banning a chemical doesn't make it disappear. DDT breaks down extremely slowly in soil, and decades of agricultural use left behind a legacy that still shows up in water supplies today. Rainwater and runoff carry trace amounts from contaminated soil into groundwater and surface water, where it can persist for generations.

The health concerns around DDT are serious and well-documented. The EPA classifies DDT as a probable human carcinogen. Long-term exposure has been linked to liver damage, reproductive harm, and disruption of the endocrine system — the network of hormones that regulates everything from metabolism to fetal development. Children and pregnant women face the greatest risk. The World Health Organization (WHO) has also flagged DDT as a chemical of concern due to its ability to accumulate in body fat over time, a process called bioaccumulation. Even low, repeated exposures can build up to harmful levels.

Current detection data shows DDT appearing in 10 water systems, with an average concentration of 0.034 parts per billion (ppb) and a maximum detected level of 0.13 ppb. The EPA's maximum contaminant level (MCL) for DDT in drinking water is 0.1 ppb — meaning that maximum detected level of 0.13 ppb actually exceeds the federal legal limit. However, the Environmental Working Group (EWG) sets its health guideline even lower, at 0.00002 ppb, based on cancer risk modeling. At the average detected level of 0.034 ppb, water containing DDT is still more than 1,700 times above the EWG's health guideline. That gap between what's legally allowed and what researchers consider safe is worth paying attention to.

Geographically, all 10 of the affected water systems in this dataset are located in Illinois. That's not a coincidence. Illinois has a long history of intensive corn and soybean farming, and DDT was heavily used on Midwestern cropland before the ban. The chemical binds tightly to soil particles, where it can linger for 30 years or more. Flooding events and heavy rainfall in the region push that contaminated soil into rivers, streams, and eventually municipal water sources. Illinois also sits atop extensive agricultural drainage tile systems, which can channel contaminated runoff directly into waterways with little natural filtration. If you live in a rural or semi-rural part of Illinois — especially near historically farmed land — DDT in your water supply is a real possibility worth investigating.

The good news is that effective filtration options exist. Activated carbon filters can reduce DDT levels, but the most reliable option is a reverse osmosis (RO) system. Reverse osmosis forces water through a semi-permeable membrane with pores small enough to block pesticide molecules, removing up to 99% of DDT and similar chlorinated compounds. An Echo Water reverse osmosis system installed under your sink gives you filtered water directly at the tap — the point where it matters most for drinking and cooking. If you're in an affected area, it's also worth requesting your utility's annual water quality report (called a Consumer Confidence Report) to see exactly what's been detected in your specific system. You can also test your own tap water independently for a more current picture. Knowing what's in your water is the first step. Filtering it out is the second.

Regulatory Standards for DDT

Cities With the Highest DDT Levels

States Most Affected by DDT

Frequently Asked Questions

Related Contaminant Guides