Local elected officials oversee critical infrastructure investments, yet limited electoral competition may weaken the alignment between local policy and residents' welfare. Using new data on investment and performance for California's drinking-water municipal utilities, we document that jurisdictions with weaker electoral competition exhibit higher water pollution and respond less to public investment aid. We then build and estimate a dynamic model in which residents differentially value water quality and vote accordingly, while office-seeking politicians weigh administrative costs against re-election prospects when choosing investments. Residents' preferences are identified from housing transactions at jurisdiction boundaries and electoral incentives are identified by exploiting variation in voter welfare gains from investment. Counterfactual increases in accountability reallocate investment toward high-need jurisdictions, reduce pollution, and generate progressive welfare gains. Limited accountability also dampens the effectiveness of federal and state subsidies by diverting funds away from high-return investments.