pf2e.fyi
From Pathfinder Howl of the Wild, which isn't enabled.

Hydration (Merfolk)

ANCESTRY FEATURE

Your body requires you to return to aquatic environments at least once in a 24-hour period. After the first 24 hours outside of water, you take a –1 status penalty to Fortitude saves. After 48 hours, you struggle to breathe air and begin to suffocate until returned to water.

Effect: Dehydrated

Pathfinder Howl of the WildORC