A water taxi or water bus, also known as a commuter boat, is a watercraft used to provide public transport, usually but not always in an urban environment. Service may be scheduled with multiple stops, operating in a similar manner to a bus, or on demand to many locations, operating in a similar manner to a taxi. A boat service shuttling between two points would normally be described as a ferry rather than a water bus or taxi.

The term water taxi is usually confined to a boat operating on demand, and water bus to a boat operating on a schedule. In North American usage, the terms are roughly synonymous.