What I Expected

Changing this spot in the sounds.json document with a resource pack would change the player drowning sound to whatever new sound chosen to replace it.

What Happened

Changing this spot does not affect the drowning sound for any entity. The sound isn't even taken from the "hurt" section, but instead from the "game.player.hurt" sound, meaning it's impossible to change the sound for one mob without changing it for all of them.

To Reproduce

Change the sound chosen in the "hurt.in.water" entry with a resource pack. Go into a world with the pack applied and go underwater until you take drowning damage. The sound you chose to play will not be the one playing.