Background Sodium (Na⁺) in saline water may increase blood pressure ( BP ), but potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺) may lower BP . We assessed the association between drinking water salinity and population BP . Methods and Results We pooled 6487 BP measurements from 2 cohorts in coastal Bangladesh. We used multilevel linear models to estimate BP differences across water salinity categories: fresh water (electrical conductivity, <0.7 mS/cm), mild salinity (electrical conductivity ≥0.7 and <2 mS/cm), and moderate salinity (electrical conductivity ≥2 and <10 mS/cm). We assessed whether salinity categories were associated with hypertension using multilevel multinomial logistic models. Models included participant-, household-, and community-level random intercepts. Models were adjusted for age, sex, body mass index ( BMI ), physical activity, smoking, household wealth, alcohol consumption, sleep hours, religion, and salt consumption. We evaluated the 24-hour urinary minerals across salinity categories, and the associations between urinary minerals and BP using multilevel linear models. Compared with fresh water drinkers, mild-salinity water drinkers had lower mean systolic BP (-1.55 [95% CI : -3.22-0.12] mm Hg) and lower mean diastolic BP (-1.26 [95% CI : -2.21--0.32] mm Hg) adjusted models. The adjusted odds ratio among mild-salinity water drinkers for stage 1 hypertension was 0.60 (95% CI : 0.43-0.84) and for stage 2 hypertension was 0.56 (95% CI : 0.46-0.89). Mild-salinity water drinkers had high urinary Ca²⁺, and Mg²⁺, and both urinary Ca²⁺ and Mg²⁺ were associated with lower BP. Conclusions Drinking mild-salinity water was associated with lower BP , which can be explained by higher intake of Ca²⁺ and Mg²⁺ through saline water.

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