Household food insecurity has emerged as a very powerful predictor of poor health among people living with HIV (PLHIV), predicting increased risk of HIV transmission as well as poor HIV outcomes. Household water insecurity (WI) may be equally or more powerfully predictive of HIV-related outcomes, but strikingly, its role in HIV outcomes has been almost entirely overlooked. Indeed, because there is currently no validated scale for assessing household access to water in sufficient quantity and quality, it has not been possible to measure the consequences of WI. Therefore, the scientific objective of this application is to elucidate the role of household WI in poor health outcomes among HIV-infected women and their infants in Nyanza, Western Kenya. This research will further the long-term goal of understanding the behavioral and psychological coping mechanisms that HIV-infected mothers use to preserve their health and that of their infants. The central hypothesis is that WI is detrimental to this population in economic, nutritional, disease, and psychosocial domains, and in ways distinct from food insecurity. This hypothesis was guided by preliminary data from the investigators’ ongoing K01-funded cohort in Nyanza, and will be tested via 3 specific aims. First, a household WI scale will be developed based on prior research and formative research in Kenya (Aim 1). It will then be piloted and validated (Aim 2). The resultant scale will then be used to assess differences in WI by HIV status and sequelae of WI among 360 women and their infants in the PI’s ongoing cohort (Aim 3). It is hypothesized that the prevalence of WI will be greater among HIV-infected women, and that it will be associated with worse outcomes, including greater viral load, diarrhea, stress, depression, and sub-optimal infant feeding practices. This research is highly significant because a) water scarcity is a widespread and growing problem, often occurring in places with high HIV prevalence; b) women bear the major burden of water acquisition and use; and c) there are a number of highly plausible and serious health consequences of WI for HIV-infected women (e.g. diarrhea) and their infants (e.g. less exclusive breastfeeding) given the compromised immunity of PLHIV, their greater water needs, and lesser abilities to access water. With a better understanding of how household WI is deleterious, it will be possible to design more effective interventions to improve the health of HIV-infected mothers and their HIV-exposed infants, as well as among people not directly impacted by HIV. This research is innovative for its use of cutting-edge qualitative and quantitative methods to develop the first validated household WI scale and because it will generate novel data to test hypotheses about the pathways by which WI may impact the health of HIV-infected mothers and their infants. The expected outcomes include the first validated household-level WI scale, which will be ready for adaptation among other populations, and an increase in our understanding of the barriers to optimal health faced by HIV-infected mothers, thereby highlighting novel ways to eventually intervene to reduce the risk of poor health outcomes among PLHIV and reduce vertical transmission of HIV.