What is the most hydrating fluid to drink? The surprising truth.
                                
                                
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                                    5 min read                                
                            
                                According to a 2015 study from Scotland's St. Andrews University, the most hydrating fluid to drink is not plain water, but skim milk. This surprising finding, measured by the Beverage Hydration Index (BHI), reveals that a fluid's nutrient composition can influence how long the body retains it.