Water prevents kidney stones. When the kidneys don't get enough water, salts may crystallize, forming painful stones. Water is the best hangover remedy. I don't suggest you drink, but if you do, drink water to get over it. Water dilutes the alcohol in your blood, which reduces the concentration in your brain, helping to relieve headache and other symptoms.
Water helps head of urinary tract problems.
A well-flushed system is less likely to be susceptible to infection. Of course, the number one reason to drink water is that it quenches your thirst. Nothing does it better. You can substitute sodas or electrolyte drinks, but none of them wets your whistle with fewer calories than water. Make it a habit to keep a glass of water near you during the day.