Rapid population growth coupled with inadequate infrastructure has called into question both human health and environmental sustainability in the U.S.-Mexico border region. Of particular concern is the lack of water and wastewater infrastructure in border colonias. Though some progress has been made in improving the situation of certain communities, many continue to live in significantly substandard conditions. This study explores the potential that rainwater harvesting may have for partially filling colonias’ safe water needs. Two objectives motivate the analysis. First, the impact rainwater harvesting might have on residents’ water budgets is measured through a simulation using information from an existing colonia in Arizona. A cost estimate of a rainwater harvesting system in the chosen colonia is also prepared so that economic comparisons with other infrastructure types might be made. Second, interviews with project funding agencies begin to explore why this alternative technology is not more widely used in locations where it appears to be a viable water-obtaining strategy. The research findings indicate that rainwater harvesting can be used to substantially and affordably increase onsite water availability in colonias, and suggests that increased attention be given to this alternative approach in infrastructure planning for especially remote and/or small colonia settlements.