It could serve in dozens of roles while "waiting" to be broken down: coolant, solvent, beverage, general environmental adjuster, swimming pool filler...
Now that you mentioned it, does it make sense for the TOS Enterprise
to have a swimming pool or not?
A couple of days ago I visited a Soviet Juliett-class sub from the early 1960's. They had a least one shower for the whole crew.
A couple of years ago I saw interior footage of the Soviet Typhoon-class. Quite in contrast to what we saw in "The Hunt for Red October" it had at least a miniature swimming pool, though I thought it rather qualified as an oversized bathtub
. (scroll to bottom of the picture collection)