Water intake is the amount of non-diuretic fluid we take in during the day. Water intake has to be monitored in order to make sure we take in the right amount. During periods of intense sweating, we need more water to replace fluids lost.
It is possible to over-hydrate though. In long distance endurance events, some athletes have been known to over-hydrate, without replacing electrolytes. This leads to an over-filling of cells and a dilution in minerals, most notably sodium. This condition is known as hyponatremia and can be very dangerous.