ASSOCIATION BETWEEN HARDNESS OF DRINKING WATER AND BLOOD PRESSURE – A COMMUNITY BASED CROSS SECTIONAL STUDY IN THENI

Abstract

Title: Association between Hardness of Drinking Water and Blood Pressure A Community Based Cross Sectional Study in Theni Background: Hypertension remains a major public health concern and is a leading risk factor for cardiovascular morbidity and mortality. Emerging evidence suggests that the mineral composition of drinking water, particularly calcium and magnesium contributing to water hardness, may influence blood pressure levels. However, findings across studies remain inconsistent. The present study aimed to assess the association between drinking water hardness and hypertension among adults residing in urban and rural areas of Theni district. Materials and Methods: A community-based cross-sectional study was conducted from October 2022 to September 2024 among 857 adults (urban: 444; rural: 413). Sociodemographic details, duration of stay, socioeconomic status (Modified B.G. Prasad scale 2025), education and occupation of the head of the family, and drinking water characteristics were collected using a structured questionnaire. Blood pressure was measured using standard procedures and classified according to JNC 8 guidelines. Drinking water samples were collected in pre-cleaned containers and analysed on the same day for hardness concentration using the SPADNS spectrophotometric method at the MDRU laboratory, GTMCH, Theni. Total dissolved solids (TDS) and calcium carbonate (CaCO₃) levels were estimated to assess water quality. Water hardness was classified as Soft (<60 mg/L), Moderately Hard (60–120 mg/L), Hard (120–180 mg/L), and Very Hard (>180 mg/L). Pearson’s correlation analysis was used to determine the relationship between CaCO₃ levels and blood pressure parameters. Univariate and multivariable logistic regression analyses were performed to identify independent predictors of hypertension. A p-value <0.05 was considered statistically significant. Data were entered in Microsoft Excel and analysed using Open Epi software version 3.01. Results: The overall prevalence of hypertension was 32.3%, and 37.5% were pre-hypertensive. Regarding water hardness, 6.5% had soft water, 36.5% moderately hard, 37.5% hard, and 19.5% very hard water exposure. CaCO₃ levels demonstrated a significant negative correlation with systolic blood pressure (r = −0.391; p < 0.001) and diastolic blood pressure (r = −0.523; p < 0.001), and a weak positive correlation with TDS (r = +0.174; p < 0.001). In univariate analysis, very hard water appeared protective against hypertension (OR 0.244; 95% CI: 0.150–0.395; p < 0.001). However, in multivariable analysis, exposure to very hard water (>180 mg/L) was independently associated with hypertension (AOR 7.013; 95% CI: 3.431–14.338; p < 0.001). Conclusion: The study demonstrated higher CaCO₃ levels were inversely correlated with systolic and diastolic blood pressure, the adjusted association between very hard water and hypertension indicates a complex, multifactorial relationship requiring further longitudinal and mechanistic investigation to inform public health policy.