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

Alachlor, commonly sold under the brand name Lasso, is a weed killer that farmers have used for decades on corn, soybeans, and other row crops. It enters drinking water primarily through agricultural runoff — when rain washes across treated fields and carries the chemical into nearby streams, rivers, and groundwater. Once alachlor reaches a water source, it can persist long enough to work its way into municipal water systems and private wells. The EPA banned most uses of alachlor in the United States in 2016, but the chemical still shows up in water supplies today, a reminder that what goes into the soil doesn't disappear overnight.

Alachlor is classified as a probable human carcinogen by the EPA. Animal studies have linked it to tumors of the nasal passages, thyroid, and stomach. At lower exposure levels, it can affect the liver, kidneys, and spleen over time. The EPA also notes that children may be more vulnerable to pesticide exposure because their bodies are still developing. These risks are why water quality researchers take even trace detections seriously, even when levels fall below legal limits.

Right now, the EPA's legal limit for alachlor in drinking water is 2 parts per billion (ppb). Across the 30 water systems where alachlor has been detected, the average level measured 0.137 ppb — well below that federal ceiling. The highest recorded level reached 1.92 ppb, just under the legal limit. None of the 30 systems exceeded the EPA's guideline. That said, "legal" doesn't always mean "safe." The EPA's limits are set with economic and technical feasibility in mind, not just pure health protection. Independent researchers argue that for probable carcinogens like alachlor, the safest target is as close to zero as possible.

Geographically, the detections follow a clear pattern tied to farming. Florida leads with 10 affected systems, followed by Wisconsin (5), Louisiana (4), Iowa (3), and Ohio (2). Iowa and Ohio sit in the heart of the Corn Belt, where row crop agriculture dominates and alachlor use was historically heaviest. Wisconsin's dairy and grain farming regions share similar soil and water dynamics. Florida and Louisiana present a slightly different picture — both states have warm, wet climates that accelerate runoff and have histories of intensive vegetable and sugarcane farming where herbicides like alachlor were widely applied. In all these states, water systems near agricultural land face the greatest exposure risk.

The good news is that effective filtration options exist. Activated carbon filtration — the kind found in many under-sink and whole-house filters — can reduce alachlor levels significantly. For the most complete protection, a reverse osmosis (RO) system is the gold standard. Reverse osmosis forces water through a semi-permeable membrane that blocks contaminants as small as individual molecules, removing up to 99% of pesticide residues including alachlor. Echo Water's reverse osmosis systems are designed specifically for this kind of protection, giving your household a reliable barrier against agricultural chemicals that standard municipal treatment may not fully eliminate. If you're on a private well in a farming region, testing your water annually is especially important — wells have no regulatory oversight, and contamination can go undetected for years. Knowing what's in your water is always the first step toward fixing it.

Regulatory Standards for Alachlor (Lasso)

Cities With the Highest Alachlor (Lasso) Levels

States Most Affected by Alachlor (Lasso)

Frequently Asked Questions

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