Endrin in Drinking Water: Complete Guide (2026)

What is Endrin and Why Does It Matter?

ENDRIN: A PERSISTENT PESTICIDE IN YOUR WATER

What Is Endrin and How Does It Get Into Tap Water?

Endrin is a synthetic pesticide that hasn't been manufactured in the United States since 1986, yet it still shows up in water supplies across the country. The chemical was once widely used to kill insects on cotton crops and other agricultural products. Because endrin breaks down slowly in the environment—it can persist for decades—it continues contaminating groundwater and surface water long after its last application. When it rains, endrin residues in soil wash into rivers and streams. From there, water treatment plants draw water that may contain trace amounts of this chemical. Endrin can also leach into groundwater from old contaminated sites, particularly in agricultural regions where the pesticide was heavily applied.

The EPA detected endrin in 48 public water systems across the country, with Florida and New York reporting the most cases (11 systems each). Kansas and Nebraska each reported 5 systems, and Oklahoma reported 4. The highest concentration found was 0.079 parts per billion (ppb), while the average across all systems was 0.012 ppb. These are very small amounts, but the question remains: is any amount of endrin safe?

Health Effects and What the Science Shows

Endrin is classified as a probable human carcinogen by the EPA, meaning long-term exposure may increase cancer risk. Animal studies show that endrin damages the nervous system, liver, and kidneys even at relatively low doses. It can also affect reproductive health and development in children exposed in the womb or during early childhood. The World Health Organization (WHO) has flagged endrin as a chemical of concern due to its persistence and toxicity.

Most people exposed to endrin through drinking water experience no immediate symptoms because the levels are so low. However, chronic exposure—drinking contaminated water over months or years—is what researchers worry about. Children are considered more vulnerable to pesticide exposure than adults because their bodies are still developing and they drink more water per pound of body weight.

The Regulatory Picture: EPA Standards vs. Real-World Protection

The EPA's drinking water limit for endrin is 2 ppb, which means water systems must treat their water if endrin exceeds this level. None of the 48 systems detected in this analysis exceeded the EPA's standard. However, the Environmental Working Group (EWG), a nonprofit that focuses on health protection, recommends a stricter guideline of 0.014 ppb based on cancer risk assessment. By this stricter standard, some of the detected systems are close to or at the EWG benchmark. The gap between EPA and EWG standards reflects a difference in how cautious you want to be—the EPA sets limits based on what's technically feasible to remove, while EWG sets health-based targets regardless of treatment difficulty.

Geographic Patterns and Why Certain Regions Are Affected

The concentration of endrin detections in Florida and New York likely reflects the agricultural history of these states and the presence of older, contaminated industrial sites. Florida's extensive citrus and vegetable farming used endrin heavily in the 1960s through 1980s. New York's detections may be tied to historical agricultural use and contaminated groundwater plumes that move slowly through soil. The Midwest detections in Kansas and Nebraska correlate with the region's heavy pesticide use on corn and wheat crops. Over time, these chemicals have migrated downward into aquifers that supply drinking water.

Removing Endrin From Your Drinking Water

If your water system detected endrin, your best protection is a home filtration system. Activated carbon filters and reverse osmosis systems both remove endrin effectively. Reverse osmosis is particularly reliable, removing up to 99.9% of endrin and other pesticide residues. If you live in Florida, New York, Kansas, Nebraska, or Oklahoma, it's worth testing your tap water or checking your local water quality report to see if endrin has been detected in your area. Contact your local water utility for their most recent water quality report, which lists all detected contaminants and their levels.

Regulatory Standards for Endrin

Cities With the Highest Endrin Levels

States Most Affected by Endrin

Frequently Asked Questions

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