Study Suggests Some Tap Water May Raise Blood Pressure

 Just bought a Brita water filter since I wasn't drinking enough water.

Study Suggests Some Tap Water May Raise Blood Pressure

Key Takeaways

• A meta-analysis showed the extent to which drinking water salinity is associated with elevated blood pressure (BP).
• The effects on systolic and diastolic BP were more pronounced in coastal regions.
• There was insufficient evidence linking water salinity to coronary heart disease and stroke.

People exposed to greater drinking water salinity tended to have higher blood pressure (BP) and a greater risk of hypertension, a large meta-analysis found.

Comparing exposure to higher versus lower drinking water salinity, there was a mean 3.22-mm Hg increase observed in systolic BP and a 2.82-mm Hg increase in diastolic BP -- and the differences were more pronounced in coastal areas where freshwater and saltwater systems sit closely together underground, reported a group led by Rajat Das Gupta, MBBS, MPH, PhD, of Vanderbilt University Medical Center in Nashville, and the University of South Carolina in Columbia.

Based on 27 studies with over 74,000 people from seven countries, a significant increase in hypertension risk was detected as well with saltier drinking water (OR 1.26, 95% CI 1.07-1.48), irrespective of age, sex, and geographical location, the investigators noted in BMJ Global Health.

The associated increases in BP may be modest at an individual level but can have significant public health effects at a population level.

"To put it in perspective, the risk level observed in this study for water salinity is like other established cardiovascular risk factors, such as low physical activity, which increases hypertension risk by approximately 15-25%," said co-author Rajiv Chowdhury, MBBS, MPhil, PhD, of Florida International University in Miami, in a press release.

Among the U.S. studies, subgroup analysis indicated a bump of 1.91 mm Hg in diastolic BP with high salinity, though no difference in systolic BP.

The researchers cited several mechanistic pathways to explain how higher sodium consumption through drinking water can result in higher BP, including changes in small resistant arteries, reduced endothelial nitric oxide, increased vascular stiffness in the large arteries, and effects on the autonomic neuronal supply and the sympathetic activity.

Salt is known to enter drinking water in several ways, including saltwater intrusion into the groundwater that supplies nearly half of the world's drinking water. Of note, Gupta and colleagues wrote, "over 3 billion people worldwide currently live in coastal or near-­coastal areas" and "most of these coastal populations are located in low-­income and middle-­income countries, where people drink water from sources with high salinity levels."

The World Health Organization has declined to set a target level for sodium in drinking water, reasoning that sodium is "not of health concern at levels found in drinking water." Concentrations above 200 mg/L are acknowledged as resulting in bad taste, however.

"Food remains the primary source of sodium for most people," Chowdhury said. "But where salinity is elevated, drinking sources may add to total intake. Checking local water quality reports if available and focusing on overall dietary sodium are practical steps, particularly for individuals who need to manage blood pressure."

The evidence was insufficient to draw ties between drinking water salinity and risk of coronary heart disease and stroke -- reflecting a key scientific need, the authors noted.

Their meta-analysis included 27 observational studies published through May 2025, including 10 U.S. studies, three in Europe, one study in Australia and Africa each, and the rest in Asia. Participants averaged 39.3 years old and 36% were women. Most studies measured salinity directly by analyzing drinking water samples.

Meta-regression analysis suggested that the increase in systolic BP with higher water salinity was significant only for Asian populations.

"This discrepancy, however, can potentially be explained by differences in baseline salinity exposure levels across settings. For example, in coastal Bangladesh, sodium concentrations in groundwater have already reached 2,600 mg/L -- that is, 2-6 fold higher than maximal levels reported in studies from Europe, North America, or Australia (where the average levels are typically below 400 mg/L level)," Gupta and colleagues cautioned.

Study authors acknowledged that most studies included in the meta-analysis relied on single assessments of exposure, so future studies should use repeated measurements.

"These results generally align with earlier narrative reviews showing significantly higher average SBP [systolic BP] and DBP [diastolic BP] levels in high salinity areas, such as coastal regions, compared with low salinity areas. Our findings are also in line with previous randomized controlled trials evidence, which shows an approximately linear relationship between sodium intake and both SBP and DBP across the entire range of dietary sodium exposure," they wrote.