impervious
Incapable of failing; unassailable.
Resistant to the effects of water.
Made of or covered with material that doesn't allow water in.
A substance or preparation for rendering cloth, leather, etc., impervious to water.
Cloth made waterproof, or any article made of such cloth, or of other waterproof material, as rubber; especially, an outer garment made of such material.
To make waterproof or water-resistant.