Backwash (saliva), the slang term for saliva or food particles that have flowed back into a drink

Backwash (album), a retrospective compilation by the group Talulah Gosh

Backwash, the process of thoroughly cleaning a pool filter pump by reversing the flow of water through it with the dirt and rinse water going to waste.

Backwash (physical phenomenon), the backwards flow of air or water

Backwash (geography), the water that rolls back down a beach after a wave has broken

Backwash (The Wire episode), an episode of the HBO television series The Wire