Objective Past research yields inconsistent evidence of disparities in environmental quality by socioeconomic status (SES), race, and/or ethnicity. Since the political significance of race/ethnicity may be contingent upon SES, this study advances environmental justice research by examining interactively the effects of race, ethnicity, and SES on environmental quality. Methods We match 2010–2013 Safe Drinking Water Act (SDWA) compliance records with demographic and economic data for U.S. local government water utilities serving populations greater than 1,000. Statistical regression isolates direct and interactive relationships between communities’ racial/ethnic populations, SES, and SDWA compliance. Results We find that community racial/ethnic composition predicts drinking water quality, but also that SES conditions the effect; specifically, black and Hispanic populations most strongly predict SDWA violations in low‐SES communities. Conclusions Our findings highlight the importance of analyzing race, ethnicity, and SES interactively in environmental justice research. Results also carry troubling implications for drinking water quality in the United States.