Magical Hydrophobia (3.5e Flaw)
From D&D Wiki
Summary: Your body rejects water.
Detriment: Whenever the character comes in contact with water, they will sublimate into a silverish mist, taking one point of damage plus their constitution modifier for every turn they are exposed to water. If they are totally immersed, they take four points of damage plus their constitution modifier per turn.
Benefit: Characters with magical hydrophobia do not thirst, or require water at all. They can choose to either gain an additional feat, or gain the ability to detect water within 30', and foretell rain up to four hours in advance. A magical Hydrophobe may, later on, choose to spend 1 feat to gain the ability to repel water. To repel water, the character must make a concentration check. If they succeed, water will be stopped 6" away from them, forming a dry bubble. While the character is repelling water, they cannot cast spells, or perform other actions that require concentration.