This study estimates the impacts of two interventions implemented as field experiments in informal settlements by Nairobi’s water and sanitation utility to improve revenue collection efficiency and last mile connection loan repayment: (i) face-to-face engagement between utility staff and customers to encourage payment and (ii) contract enforcement for service disconnection due to nonpayment in the form of transparent and credible disconnection notices. While there is no effect of the engagement, the study finds large effects of enforcement on payment. There is no effect on access to water, perceptions of utility fairness or quality of service delivery, on the relationships between tenants and property owners, or on tenant mental well-being nine months after the intervention. To counterbalance the increase in payments, property owners increased rental income by renting out additional space. Taken together these results suggest that transparent contract enforcement was effective at improving revenue collection efficiency without incurring large social or political costs.