From Pathfinder Lost Omens Absalom, City of Lost Omens, which isn't enabled.

Replenishing Hydration

FEAT 9

You draw life from the water around you. If you submerge in water and rest for 10 minutes, you regain Hit Points equal to your Constitution modifier × half your level.

Pathfinder Lost Omens Absalom, City of Lost OmensOGL