Ah, pretty easy to make a nude humanoid figure water tight after you weld the body seams, if required, depending on how the geometries body part groups are stored... just requires some extruding, bridging and/or more welding/merging verts. As vilters said clothed figures an entirely different matter, practically impossible IMO (in terms of work required) and then the level of impossibility depending on the specific article.Consider that the clothing must be merged into the mesh not just intersect.

Hair, another matter.