Not all pesticides move through the environment the same way. Some bind tightly to soil particles and rarely reach water supplies. Others are highly water-soluble and mobile, making them more likely to leach or run off. The pesticides most frequently detected in Midwest groundwater and surface water reflect the crop mix of the region.

Atrazine is the most commonly detected pesticide in U.S. surface water and one of the most frequently found in Midwest groundwater. It's a herbicide used primarily on corn, and it's highly water-soluble. Levels in surface water often spike during spring planting season. Metolachlor, acetochlor, alachlor, and simazine are additional herbicides commonly associated with row crop agriculture that appear in regional water monitoring data. Organophosphate insecticides, though less persistent than older compounds like DDT, can also appear in water supplies during and after application periods. The 1,3-dichloropropene and trans-1,3-dichloropropene compounds in our testing panels are fumigant-related pesticides that can appear in agricultural groundwater as well.

National groundwater studies have found detectable pesticide compounds in roughly 60 percent of wells sampled in agricultural watersheds. The good news is that concentrations exceeding federal health benchmarks are found in only about 1 percent of those wells — municipal treatment systems are generally effective at reducing pesticide concentrations in surface water before it reaches the tap. The more significant concern is for private well owners, whose water is not treated and may not have been tested recently or at all.

Seasonal variation is an important factor that standard water testing often misses. Pesticide levels in both surface water and groundwater tend to peak during and shortly after spring planting, when applications are heaviest and rainfall runoff is common. A single test taken in the fall or winter may not reflect the worst-case exposure a household actually experiences. For well owners in agricultural areas, testing during or just after the spring application season gives a more representative picture.

Health effects from pesticide exposure in drinking water depend heavily on the specific compound, the concentration, and the duration of exposure. Acute effects from high-level exposure are rare from drinking water at regulatory levels. The primary concern is long-term, low-level chronic exposure — the kind that accumulates over years of daily consumption.

Atrazine has received significant research attention due to its persistence and prevalence. It has been associated with endocrine disruption, particularly effects on hormone regulation, and some studies have linked chronic exposure to increased cancer risk, though the research is ongoing and results are not fully settled. The EPA's MCL for atrazine is 3 parts per billion. Organophosphate pesticides affect the nervous system by inhibiting acetylcholinesterase — an enzyme essential for normal nerve function. Children are particularly sensitive to organophosphate exposure, and developmental neurological effects have been documented at levels of concern. Various herbicides and insecticides carry individual profiles of liver, kidney, nervous system, and endocrine effects depending on the compound. EPA has established MCLs for approximately 24 pesticides in drinking water, with health advisories for many additional compounds.

One underappreciated aspect of pesticide exposure in water is the mixture effect. Regulatory standards are set for individual compounds, but real-world exposure typically involves multiple pesticides simultaneously. Research on the combined effects of pesticide mixtures in drinking water is limited, and current standards don't fully address potential additive or synergistic effects.

Municipal water treatment systems are generally effective at reducing many pesticide concentrations, but effectiveness varies considerably by compound and treatment technology. Standard coagulation, flocculation, and filtration processes remove some pesticides but are largely ineffective against the highly water-soluble herbicides like atrazine that are most prevalent in Midwest source water. Chlorination does not reliably degrade most pesticides and in some cases can produce transformation products.

Granular activated carbon (GAC) treatment is the most effective conventional technology for pesticide reduction, and some larger treatment facilities in the region use it. However, not all municipal systems have GAC capability, and those that do may not achieve complete removal of all compounds. The only way to know what's actually coming out of your tap — after treatment — is to test it.

Pesticide testing requires a specific analytical panel — standard metals or minerals tests will not detect herbicides or insecticides. Our Clarity and Certainty consultation packages include a comprehensive VOC and pesticide panel using EPA Method 524.2, covering the 1,3-dichloropropene compounds and a broad range of additional pesticide-related analytes. If your primary concern is agricultural pesticide exposure, this panel gives you a data-driven baseline to work from.

For private well owners in agricultural areas, we recommend testing during the spring runoff season when levels are most likely to be elevated, and using that result — rather than a midwinter sample — as your decision baseline. If pesticide compounds are detected at concerning levels, activated carbon filtration is the primary treatment approach for most herbicides and insecticides. A properly sized and certified carbon block or GAC system at the point of use provides meaningful reduction for most of the compounds of concern in agricultural water. System selection should be based on your actual test results and the specific compounds present.