A fsh.
Actually, fish DO breathe; it’s just water and not air (breathing and respiration are not solely air-related). And only saltwater fish drink water, though I haven’t found exactly how that works since drinking requires swallowing the liquid, and no descriptions I found went beyond the step where a saltwater fish’s gills filter the salt from the water they take in.
*2nd comment: Riddles normally don’t have completely logical answers ^.-
But tbh fish do not have lungs, they do not technically breathe, they filter oxygen through their gills by opening and closing their mouths. I think it’s just a human tendency to call it “breathing” when it’s really just “filtering”.
More correctly, the fish is respirating - the exchange of gasses at a cellular level. Breathing is the mechanical exchange or movement of atmospheric air.
and actually, fish don’t constantly drink the water. It never goes into their stomachs until they want it to.