Simple achievement: When you load into your game you will be spawned on a random floor (1-6). Walk around the room, if there isn’t any in the room you are spawned in, go into another room by going up or down floor by looking for staircases. But eventually you will come across a the pool and give the option to drink it, press
and the achievement should pop up.
EDIT: I forgot to mention that the game is RNG based so there is no for sure location of where the pool might be located