Investigating the relationship between agricultural water usage and water quality in California

California has a highly developed agriculture system, but it faces many challenges associated with water supply and water quality. This research examines the relationship between agricultural water use and water quality at multiple scales, including a comparison of southern and northern California, analysis of seven regions, and four counties within the Central Valley, which accounts for more than 70% of agricultural water use in the state. Statistical analyses of georeferenced data from USGS and CIMIS were used to test the hypothesis that higher agricultural water use is associated with lower water quality. Results indicate that while there is no significant difference in water quality between southern and northern California, there are significant differences among regions. Furthermore, within the Central Valley, there is a significant inverse relationship between agricultural water use and two of three water quality indicators, namely dissolved oxygen and dissolved nitrate. Although further research is necessary to establish causality, these findings suggest that policymakers need to consider the effects of water use on water quality in planning California’s future agricultural development.