The average person needs need about 2.5 liters of water a day. That amount obviously differs by what people eat, where they live, how big they are and what they are doing. But researchers ignored that the most of this quantity is contained in prepared foods.
     Prospective studies fail to find benefits in kidney function or all-cause mortality when healthy people increase their fluid intake. Randomized controlled trials fail to find benefits as well, with the exception of specific cases — for example, preventing the recurrence of some kinds of kidney stones .
     Anyway, Plain water is better than a drink, if we speak about sweet drinks.