Although I have seen wallcovering pasted directly to the drywall at a large htel, almost all installer use an undercoater (Usually oil-base enamel undercoat0 to seal the wall prior to hanging. Not only does it protect the wall, it makes the wallcovering slide easier on installation. So, your wall should be protected against getting wet.
I have always used DIF brand Wallpaper Remover Solution. It is a concentrate, so 1-quart will suffice for an average size room. Put the HOT water in the sprayer first, then add th DIF. Otherwise it bubbles up like dish detergent. It helps deactivate the paste, making it a better choice than plain water.