What is "water key"

n. 1 A valve or tap for the drainage of accumulated fluid from musical instruments such as trombones or trumpets; a spit valve. 2 A rod used to open and close a buried quarter-turn water valve, as in a water main.

A water key is a valve or tap used to allow the drainage of accumulated fluid, consisting of condensed breath moisture, from musical instruments such as trombones or trumpets. It is otherwise known as a water valve or, less euphemistically, a spit valve. In valved instruments, they are found always on the main tuning slide, and sometimes on valve slides. On the trombone, it is on the downwind side of the bend in the hand slide. Baritone saxophones have a water key at the bottom of the loop at the top of the instrument.

They are often erroneously referred to as "spit valves", as the myth persists that some or much of the liquid consists of spit. It doesn't. The amount of water accumulated is directly in proportion to the size of the instrument, and the amount of metal exposed to the air, which in turn enables the process of condensation due warm, moist air from the lungs meeting metal cooled by room-temperature air.