Hey!
I suggest using water that is neutral to your touch, doesn't feel warm or cool. That is typically about 85 degrees. Sterlite tubs/containers are good for keeping them in the water because most will try to get out if they can, unless they're severely dehydrated.
You want the water to be just a tad higher than the snake's back, just covering it. If it's too deep they might panic about having a hard time keeping their head out of the water and not eventually settle down to soak.
I doubt that the dry spot on it's back is due from dehydration. Dehydration in hatchlings up to a few months old or so usually shows in the form of wrinkled skin.
Is there a chance it got burned by the basking beam or on the light itself? Kinda sounds like it. Constant soaking in that case could do more damage than good. Silvadene, neosporin or even a couple of daily applications of diluted original Listerine (50/50) work good in cases of burns or wounds.
Catch ya later!
Mike
-----
Due to political correctness run amuck,
this ol' hillbilly is now referred to as an:
Appalachian American

www.natures-signature.com