Alachlor (Lasso) in Drinking Water: Complete Guide (2026)

What is Alachlor (Lasso) and Why Does It Matter?

ALACHLOR: A HERBICIDE IN YOUR WATER SUPPLY

What Is Alachlor and How Does It Get Into Our Water?

Alachlor is a herbicide sold under the brand name Lasso, used primarily on corn and soybean crops across the American Midwest and South. Farmers spray it directly on fields to prevent weeds from competing with their crops. When it rains, alachlor doesn't stay put—it leaches into groundwater and runs off into surface water sources that feed municipal water systems. Because it breaks down slowly in the environment, it can persist in water for months or years. The EPA first detected alachlor in drinking water supplies during the 1980s and has monitored it ever since. Today, 32 water systems across the United States have detected alachlor, with levels averaging 0.128 ppb (parts per billion), though one system recorded a peak of 1.92 ppb.

Health Effects and Exposure Risks

The EPA classifies alachlor as a probable human carcinogen based on studies showing it caused tumors in laboratory animals. Long-term exposure to alachlor has been linked to increased cancer risk in humans, particularly stomach and lung cancers, according to the Environmental Working Group (EWG). Short-term exposure can cause eye irritation, skin rashes, and respiratory symptoms in sensitive individuals. Children are of particular concern because their bodies are still developing and they're more vulnerable to carcinogenic substances. The good news: the levels currently detected in most U.S. water systems remain below the EPA's legal drinking water limit of 2 ppb. However, the EWG's health guideline is 0.1 ppb—stricter than the EPA standard. This means some families are drinking water that exceeds EWG's recommendation for long-term safety, even if it's technically legal.

EPA Standards vs. Stricter Guidelines

The EPA set its maximum contaminant level (MCL) for alachlor at 2 ppb in 1994. This standard is based on acceptable cancer risk levels, but "acceptable" to the EPA means a risk of one additional cancer case per one million people over a lifetime—a threshold many health advocates consider too lenient. The EWG, which reviews the latest peer-reviewed research, recommends a much lower level of 0.1 ppb. None of the 32 detected systems currently exceed the EPA's 2 ppb limit, so they're in compliance with federal law. However, if you're in one of these systems and your water contains alachlor above 0.1 ppb, you're exposed to levels that independent health researchers consider concerning for long-term consumption.

Where Alachlor Shows Up Most

Florida leads with 11 water systems detecting alachlor, followed by Louisiana and Wisconsin with 5 systems each. Iowa and Ohio round out the top five states with 3 and 2 systems respectively. This geographic pattern reflects where alachlor is most heavily used: the corn and soybean belt stretching from the Midwest down through the Mississippi River valley into the South. Florida's high numbers likely reflect both agricultural use in central Florida and the state's vulnerable groundwater—the porous limestone aquifer that supplies drinking water to much of the state allows contaminants to seep through easily. If you live in these agricultural regions, your water system is more likely to have tested positive for alachlor at some point.

Removing Alachlor From Your Drinking Water

Fortunately, alachlor responds well to several filtration methods. Granular activated carbon (GAC) filters are highly effective, removing up to 95% of alachlor when properly maintained and replaced regularly. Reverse osmosis systems remove even more—typically 99% or better. If your water system has detected alachlor, ask your local water utility for their most recent water quality report to see current levels. If levels are above 0.1 ppb or if you simply prefer not to take chances, installing a point-of-use filter like reverse osmosis or activated carbon at your kitchen sink provides reliable protection for drinking and cooking water. For families in affected areas, this is a practical step that gives you direct control over your water safety.

Regulatory Standards for Alachlor (Lasso)

Cities With the Highest Alachlor (Lasso) Levels

States Most Affected by Alachlor (Lasso)

Frequently Asked Questions

Related Contaminant Guides