Lord of the Rings: The Return of the King - Water on Mount Doom
On the part when Sam and Frodo are on mount doom, Gollum attacks them, after Sam cuts him with his sword you see Frodo running up mount doom, at this point, look behind Frodo and you can see water on mount doom.
I would have thought that water n mount doom would have evaporated.
In the book it mentions, if I remember correctly, Sam and Frodo finding water in Mordor. (I think they drink some because ther's nothing else and they have to or else die of thirst.. once again not sure). It does seem odd that it would be on the side of a volcano... but I dont see why it isn't possible.