PHYSIC HELP! WATER TEMPERATURE?

A small reservoir has a volume of 1 cubic kilometer of water at 20 degrees Celsius. Suppose 1 million tons of TNT are detonated deep within the reservoir. If all of the energy from the resulting explosion goes into heating the water, what is the water temperature the next day? (1 ton of TNT releases 4.184�109 J of energy when detonated, and the density of water is 1000 Kg per cubic meter).