This paper evaluates the effects of adopting Best Management Practices (BMPs) on groundwater quality in the Ontario (Oregon) HUA by incorporating time lags associated with nitrate leaching and groundwater flow. Results indicate that the Federal drinking water standard of no more than 10 ppm may be accomplished in 12 years by adopting improved irrigation systems such as auto-cutback systems or solid-set sprinkler systems. However, the adoption of both improved irrigation systems and nutrient management systems, such as sidedressing and ceasing fall fertilization, would be necessary to meet the strict Oregon drinking water standard of 7 ppm.