I think all your life you might have received suggestions from your parents, friends and colleagues about drinking a lot of water in order to boost your metabolism. Well, these suggestions are indeed important but should not be taken at face value. You must determine about your daily water intake, depending upon your age, daily-activity-levels, climate in which you live and other factors.
Don't just blindly follow any routine involving great water intake.
It's a fact that there have been cases of deaths due to excessive water intake. The condition which caused these deaths is known as Hyponatremia and it's because sodium concentration in the serum dips to fatal levels because of too quick consumption of large quantities of water. It's very rare, still a possibility, especially in water drinking contests, where ignorant hosts risk lives of contestants(who are equally ignorant!) It also happens in the athletic activities like marathons where athletes keep on consuming a lot of water without replenishing their bodies with Sodium.
The death is caused by the Osmosis, because, cells(especially brain cells called 'neurons,') which have relatively higher concentration of Sodium, let more water come into them and swell, and since size of skull is constant brain cannot expand and this results in death.
Therefore be very careful about not drinking too much too fast. It's not drinking too much water which kills you, but drinking too much of it in a very short span of time. Too much of a good thing is a bad thing. Your kidneys can process upto 15 litres of water in a day! But make sure that if you drink water very often, then you go to urinals as often as well and you don't let all of the electrolytes and salts get flushed away from your system.