Alachlor (Lasso) is a pre-emergent herbicide used in the production of corn and soybeans. U.S. EPA has studied control of alachlor in drinking water treatment processes to define treatability before setting maximum contaminant levels and to assist water utilities in selecting control processes. Control can be achieved with activated carbon adsorption. The choice of granular or powdered carbon will be site specific depending on source water quality and water quality goals. Ozonation and reverse osmosis are effective control processes. After further study, they may be found to be cost-competitive alternatives to adsorption. Aeration, clarification, filtration, softening and oxidation with chlorine, chlorine dioxide, hydrogen peroxide and potassium permanganate will not provide control of alachlor under water-treatment plant conditions.