There are different methods to waterproof bathroom wood but using a sealant is one of the best methods to do so.
Sealers can waterproof the wood, they can also prevent wooden surfaces from getting scratched. They are often a clear/transparent finish that coats the wood’s exterior surface.
Sealants such as polyurethane, varnish, and lacquer give excellent waterproofing. They’re brushed or sprayed over sanded, clean wood, then softly re-sanded and re-coated when they’ve dried fully. They offer high moisture resistance compared to the oil finish.