Water isn't the most hydrating drink—here's what is

As a record-shattering heat wave grips much of the eastern United States, staying cool isn’t just about comfort—it’s about health and safety. On Tuesday, June 24, temperatures were forecast to soar near 100°F across major cities from St. Louis to Boston, according to the National Weather Service. Cities like Washington, D.C., Philadelphia, and New York were on track to see their first June triple-digit days in decades, AccuWeather reported.

Power outages, hospitalizations, and relentless humidity have put millions at risk. In the face of this extreme heat, there’s one vital defense: hydration. But despite what most people assume, plain water isn’t the most hydrating option.

Milk tops the hydration charts—here’s why
Sure, water is the go-to drink during scorching summer days. But according to a 2015 study conducted by researchers at Scotland’s St. Andrews University, it doesn’t top the list when it comes to long-lasting hydration. The study, published in the American Journal of Clinical Nutrition, evaluated the hydration effects of 13 common beverages and found that skim milk and oral rehydration solutions like those used for diarrhea were more effective at keeping the body hydrated than plain water, still or sparkling.


Why? According to the study: the volume consumed and the nutrient composition of the drink. Milk contains not just water but also lactose (sugar), protein, fat, and sodium. This combination slows down how quickly the stomach empties, which means fluids are released into the bloodstream more gradually and retained longer. Sodium, in particular, helps the body hold on to fluid like a sponge, resulting in less frequent urination and more efficient hydration.

Similarly, oral rehydration solutions—which include a careful mix of water, salt (sodium), potassium, and a small amount of sugar—have been scientifically designed to promote maximum fluid retention.

Choose wisely: Not all beverages are created equal
That doesn’t mean all flavored or sugary drinks are hydration heroes. Beverages high in concentrated sugars—like fruit juices and sodas—don’t hydrate as well. Once they reach the small intestine, their high sugar content triggers a process called osmosis, pulling water from the body into the intestine to dilute the sugars. Ironically, this means that drinking too much soda can actually dehydrate you.


If your options are soda or water, experts still advise choosing plain water. It may not stay in your system as long as milk, but it helps your kidneys and liver flush out toxins, keeps your skin supple, and supports every major function in your body.

Most importantly, staying hydrated—especially during a brutal heatwave—keeps joints lubricated, helps fight infections, and ensures nutrients reach your cells.