Immersion diuresis is a type of diuresis caused by immersion of the body in water (or equivalent liquid). It is mainly caused by lower temperature and by pressure.

The temperature component is caused by water drawing heat away from the body and causing vasoconstriction of the cutaneous blood vessels within the body to conserve heat. The body detects an increase in the blood pressure and inhibits the release of vasopressin, causing an increase in the production of urine.

The pressure component is caused by the hydrostatic pressure of the water directly increasing blood pressure. Its significance is indicated by the fact that the temperature of the water doesn't substantially affect the rate of diuresis. Partial immersion of only the limbs does not cause increased urination. Thus, the hand in warm water trick (immersing the hand of a sleeping person in water in order to make him/her urinate) has no support from the mechanism of immersion diuresis. On the other hand, sitting up to the neck in a pool for a few hours, clearly increases the excretion of water, salts, and urea.