Well, studies have proven that drinking water isn't enough to keep our body hydrated during an intense activity. Look for drinks that contains high electrolytes because it can really help a lot on hydrating our body.
Like this one for instance:
The hydration ability of three commercially available sports drinks and water.
Because of the lack of differences found at 100% absorption time, both at rest and during exercise, compared with water, the sports drinks studied in this research did not appear to hydrate the body at a faster rate