The US-Mexico border divides the communities of Palomas, Chihuahua and Columbus, New Mexico, but they remain intimately linked. Both communities suffer from inadequate social services, poor public infrastructure, high unemployment and high poverty rates. To confront these challenges, Palomas and Columbus work together, sharing resources like hospitals, firefighters, and even schools. Palomas and Columbus also share another vital resource—groundwater. In the parched Chihuahuan desert, the communities depend on this groundwater as their sole water supply source, yet their aquifer is contaminated with arsenic and fluoride. Local governments acknowledged this contamination as early as the 1970s, but it was not until the 2000s that they received the needed reverse osmosis technology and water/wastewater infrastructure to ameliorate household exposure to water contamination. This thesis compares how Columbus and Palomas have addressed water insecurity over a twenty-year period from 1996-2016, using a 1996 study as the baseline (Tanski et al. 1998). New data include a household survey of 152 households, 60 semi-structured interviews, and participant observations of water practices collected during two months of fieldwork in the summer of 2016. The central research questions of this thesis are Q1) What causes household water insecurity on the US-Mexico border? and Q2) How can water policymakers and providers more equitably provide users with access to clean, reliable, and affordable drinking water? From a human development perspective, water security is defined as having an adequate supply of reliable and affordable water for a healthy life. This thesis uses a political ecological lens to more critically examine how water security connects to socio-political processes of water governance and power imbalances. Following Jepson (2014), this thesis argues that water (in)security is produced by problems in water access, water quality, and water affect (or water distress) and unfolds within a complex, hydrosocial landscape. Applying Jepson’s (2014) water security typology to Columbus and Palomas revealed that each local water utility adopted a distinct approach to addressing groundwater contamination, predicated on their financial and social resources, and structured by national and bi-national water policies as well as their institutional parameters. The survey found household water security has improved in terms of water access and reliability. But, centralized water filtration technology increased costs and reduced affordability in Columbus, while decentralized water filtration technology inadequately resolved household water supply contamination in Palomas. Thus, despite the technological improvements, households remain unevenly exposed to water contamination and costs. This raises concern about approaches to water security, which should be more finely attuned to water equity. Water equity means the rights to access clean water are more equitably distributed within the communities, and there is greater recognition/participation of community members in decision making on water management.