noun, noun which may take the genitive case particle 'no'
underwater; below the water surface
Literal physical location beneath the surface of water.
Watch out for rocks below the water surface.
noun, noun which may take the genitive case particle 'no'
behind the scenes; behind closed doors; below the surface
Figurative use for activities or negotiations that are not publicly visible; often implies hidden maneuvering or preliminary work.
Negotiations are continuing behind the scenes.
Compound of 水面 (water surface) + 下 (under, below). The figurative sense extends the idea of something hidden beneath the surface.