Depends where. In the desert -sandman, in the sea Hydro man. They'll just clash and turn into a giant mud-monster and the human-torch will come along and bake them/it dry!!
I don't know a whole lot about either, though from what I know I'd say Hydro man would win as he can wash away (with enough pressure and time) Sand man. Of course how do you kill either Sandman or Hydro?
Sandman is made of sand and Hydro man is made of water so how exactly would one hurt the other? Hydroman can wash away Sandman, but he'll just reform right? Same goes for Hydroman, smash his form and he'll just reform right?
Heres when it really happened guys: 'during a battle with hydro-man, sandman somehow became merged with his watery counterpart to form a giant mud-like monster.spiderman defeated this monster and the two criminals were thought to be dead, until the mud spread months later'.that was from my spiey guide- a beautiful book. I'm not as sad as you'd think, my comics are in the same room as the computer!!Nah!!I'm lying, I'm sad!!
And Castles Made of Sand, falls into the sea, eventually. So Hydroman will get all powered up with the water around them in the sea, thus he'll easily overpower Sandy and win.
They should fight on a beach that way there is plenty of water and sand for both of them and under those conditions they are evenly matched and it can go either way but I would have to say that sandman would win because he has more fighting experience than hydroman.