Thermostat

Cougar 99, 113,745 miles one of this days I was driving my car like I always do and suddenly the needle that read the temperature in the gauge went all the way to the H, so I thought that my car needed some water, I poored water in the water pump but then It took like 5 minutes for the car to get hot again, I check thewater pump and the car still have water. I don't know what the matter is I think It could be the water pump, thermostat that is that letting go the water throught the radiator or some like.