Into the Depths

Underwater – Depth and Temperature

The water’s depth and temperature will determine a character’s survivability when they are under the water.

DAMAGE FROM WATER PRESSURE

The deeper a character ventures down into the water, the greater the water pressure. Freedom of movement and water breathing will not protect characters from either the crushing effects of deep water or the effects of cold. The indicated Constitution saves must be made one round after being at a certain depth. If the save is failed, then the damage is taken and another save must be made each minute until the character makes a Constitution save, after which further saves are not necessary. The character is then considered acclimated to that depth. Descending to a deeper depth range as indicated on the table, however, requires another saving throw be made.

DAMAGE FROM COLD WATER TEMPERATURE

Water conducts heat much more efficiently than air; therefore cold water causes much greater loss of body temperature than does cold air. It is also important for DMs to note that water becomes heavier as it cools until it reaches a temperature of about 37 degrees Fahrenheit (just above freezing). Below 37 degrees, as water crystallizes into ice, it becomes lighter so that ice will float on the surface of the water. Therefore, the bottom of any large body of water will tend to remain at 37 degrees F most of the year. The above table outlines the necessary saves and resultant cold damage from being in water at various temperatures. Unlike pressure, Constitution saves against cold damage from water must be made each minute, even after a successful save. The table assumes that the creature is not wearing anything that will provide meaningful insulation while in water. Normal clothing or armor is of no benefit. A creature wearing a watertight outfit that captures a layer of water next to the skin (like a wet suit) has advantage on Constitution checks against the cold damage. Smearing the skin with grease or fat, which repels water, will provide a +5 bonus to the necessary Constitution saves. Of course, magical forms of protection from cold also apply.