Drinking water salinity in a hot-dry environment: Hydration, kidney function, and blood pressure - The increasing salinity of groundwater is a key emerging global environmental health risk factor for hundreds of millions of adults, including in the United States. Droughts, saltwater intrusion, and anthropogenic effects are exacerbating the salinization of drinking water sources. Drinking water salinity increases concerns about water safety. Further, recent evidence suggests that it may affect body water homeostasis, negatively impact kidney function, and increase blood pressure (BP) and risk of hypertension. In hot settings, physiological water needs increase, yet water scarcity and salinity make it harder to meet those needs. However, aside from guidelines for palatability, which are important as they may signify individual concerns, there are currently no established health standards for maximum water salinity (unlike dietary salt). Much of the research examining drinking water salinity has done so cross-sectionally, retrospectively, or in settings where other factors such as health-protecting salts may confound the relationship. Further, in examining chronic kidney disease of unknown origin, studies examine water quality or heat stress, without integrating co-exposures. Thus, it is hard to know how drinking water salinity affects hydration, kidney function, and hypertension and whether effects are due to salinity or other factors. A critical step toward understanding and mitigating the health risks of water salinity is to establish evidence-based relationships between water salinity and health using a longitudinal design in a real world hot setting with variation in water salinity levels due to seasonality, hydrology, and a desalination system. This research proposes to test the central hypothesis that drinking water salinity is detrimental to hydration, kidney function, and BP longitudinally. The specific aims of the project are: (1) To identify seasonal variation in drinking water salinity and individual hydration status, water turnover, and water insecurity; (2) To test how drinking water salinity affects kidney function and injury over time; and (3) To test how drinking water salinity affects systolic and diastolic BP and hypertension longitudinally, and whether these BP changes affect kidney health. The research will expand an ongoing longitudinal study to leverage a natural experiment created by a new water desalination system that provides variation in drinking water salinity levels across communities. This longitudinal study will enroll 600 adults (300 men, 300 women; 50% aged 18-45; 50% aged 45+) with seasonal (dry and rainy) assessments across 3 years to have within-participant, repeated measures analysis. The research will integrate environmental measures of water quality (in-field and laboratory assessment of water salinity, ionic composition, and heavy metals) and heat stress (wet bulb globe temperatures, heat illness), socio-ecologic assessments (in-depth multi-modal measurements of water and food insecurity, socio-demographics, diet, mobility, and stressors), and health measures using point-of-care and gold-standard laboratory methods (biomarkers of hydration, water turnover, kidney function/injury, and BP). The results will inform policy and EPA and WHO recommendations about drinking water salinity levels for human health and potential mitigation with water desalination in all affected areas.
