I agree with JandC_Reptiles, you dont want to dip the snake straight into cold water. I think luke warm water or water at room temps would be better. I'd keep it in the water for an hour and see how it goes. After that i would put it back in its enclosure with no heat, just room temps.
Unfortunately such a traumatic ordeal like overheating could possibly lead to neurological problems, lack of co-ordination and death of the animal within the next few days. You'll just have to leave it alone and let it sort itself out.
It may be a good idea to tube feed it some fluids to help hydrate it.