Pesticides are important for agricultural productivity, but that doesn't mean they lack drawbacks. Drinking water contamination is one potential problem, especially in agricultural regions. If lab tests show your well water has been contaminated, reverse osmosis is one possible treatment option.
Reverse osmosis removes contaminants from water by forcing it through membranes that allow the water molecules but not the contaminants to pass. According to the EPA, reverse osmosis has been demonstrated to be highly effective in removing some pesticides, but specific data on many pesticides is not available.
The effectiveness of a reverse osmosis process depends on the type of membrane, the design of the system and the type of pesticide contaminant. Thin film composites are better in general than cellulose acetate or polyamide; nonetheless, even thin-film composite membranes will not necessarily remove all pesticides. According to the EPA, tests with thin-film composites removed from 80 percent to 100 percent of triazine, 98.5 percent to 100 percent of acetanilide, 100 percent of organochlorine pesticides, 98.5 percent to 100 percent of organophosphorus pesticides, and over 92.9 percent of carbamate pesticides from drinking water.
Clearly, reverse osmosis membranes are better at removing some pesticides -- especially organochlorines and acetanilides -- than others. Granular activated carbon filtration is another option that may provide superior performance for some classes of pesticides. If you find that your well water is contaminated, your best bet will be to contact a local water treatment specialist, who can provide you with a recommendation based on the type of contaminants in your water.