In the United States, underbounded communities—urban disadvantaged unincorporated neighborhoods characterized by high-poverty and high residential density lying just outside the border of an incorporated municipality—often lack consistent access to clean and safe water. Poor water quality and inadequate infrastructure shape residents’ risk perceptions, often leading to tap water mistrust, but little is known about the broader social, political, and economic drivers of water quality in these settings or about how such drivers inform the social construction of risk across different stakeholder groups. Using an underbounded African-American/Hispanic neighborhood in the Tampa Bay metropolitan region as a case study, we illustrate how tap water mistrust is socially constructed and how these constructions contrast between neighborhood residents and government officials. Interviews and participant observation with these groups reveal that tap water mistrust emerges from the nexus of inadequate infrastructure, poor housing conditions, challenges relating to the affordability of piped water, and jurisdictional disconnects. We call for interventions that foreground participatory research, integrate social and cultural context into technical solutions, and prioritize equitability in decision making.