We investigate the relationships between water quality and socioeconomic factors in California at the county level for the years 1993 to 2006 using 24 water quality indicators coming from seven different types of water bodies. We estimate these relationships using three classes of models: the traditional per capita income-pollution level - Environmental Kuznets Curve (EKC) - specifications, a more inclusive model containing main socioeconomic variables such as agricultural intensity, land use, ethnic composition, population density and educational attainment, and a model that includes the socioeconomic variables while accounting for spatial correlations too. For most water quality indicators, we do not find support for EKC specifications. For pollutants like phosphorus and total suspended solids, the level of agricultural activity is a significant determinant of water quality in California, but for other surface water pollutants commonly considered agricultural pollutants, such as ammonia and nitrate, the level of agricultural activity is not statistically significant. We find that education, ethnic composition, age structure, land use, population density, and water area are all significantly correlated with various indicators of water quality.