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D&D 5E – House Rules – Underwater -Depth and Temperature

uNDERWATER

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

Depth CON Save Points of Damage
0-200 ft  none  none
201-250 ft  DC 10  1d6/minute
251-300 ft  DC 15  2d6/minute
301-400 ft  DC 20  3d6/minute
401-500 ft  DC 25  4d6/minute
501-1000 ft DC 30 5d6/minute
1001 ft or deeper DC 35  6d6/minute

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

Temperature  Degree F  CON Save  Points of Cold Damage
Tropical  >86  none  none
Warm  65-85  none  none
Cold  55-64  DC 10  1d6/minute
Frigid  45-54  DC 15  2d6/minute
Icy  32-44  DC 20  4d6/minute

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.

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2 responses to “D&D 5E – House Rules – Underwater -Depth and Temperature

  1. Richard Hayden April 1, 2017 at 6:42 am

    Nice rules in general but a little harsh on the cold water damage. Check this: https://www.google.co.uk/search?sourceid=chrome-psyapi2&ion=1&espv=2&ie=UTF-8&q=how%20long%20can%20the%20average%20person%20survive%20in%20freezing%20water&oq=how%20long%20can%20the%20average%20person%20survive%20in%20freezing%20water&aqs=chrome..69i57.17643j0j7

    I’d suggest giving each temperature bracket a time period that can be survived before damage starts being incurred.

    • Ronny April 1, 2017 at 10:55 am

      Richard,
      Thanks for the link to “How long can a person survive in cold water?”.
      Adding a time period before taking any damage is a reasonable rule. But I think adding +5 to the con saves would more accurately reflect the information on your table.

      I am amazed at how closely that table matches mine.
      Here is what I mean –

      Icy
      32-44(mine) vs 32.4-40(theirs)
      4d6/minute(mine) vs. 15-30 minutes(theirs)

      Frigid
      45-54(mine) vs. 40-50(theirs)
      2d6/minute(mine) vs 30-60 minutes(theirs)

      Cold
      55-64(mine) vs. 50-60(theirs)
      1d6/minute(mine) vs. 1-2 hours(theirs)

      The problem I see with their table is the range of times. It looks like they are saying, for example, that you couldn’t become exhausted or unconscious in 40-50 degree water in less than 30 minutes. I must assume that they really mean then it would typically take you from 30 to 60 minutes. I don’t think that it would be unreasonable to assume that a PC with low hit points and low constitution might die in as little as 10 minutes.

      I would say that unconsciousness underwater = reaching 0 hit points.

      Using a PC with a lot of hit points is illuminating. A 20th level fighter with typical hit points and no constitution modifier would have 124 hit points. Using my table, in any temp. of water, if he failed his con save each minute and took the minimum damage, he would survive the length of time indicate by your table, but one more failed save and he would die. If that same character failed his con save each minute and received the maximum amount of damage, he would die in about one third of the minimum time listed on your table. This is where your delayed onset of damage rule would help. Even though he is not likely to fail his con save every time, by giving him a +5 bonus to his con save should allow him to save often enough to make up the difference. Another option would be to allow him to take advantage on his saves.

      Here are my numbers:

      If he failed his CON save and received minimum damage each minute the maximum time he could survive is the same as indicated on your table, but no longer:
      Icy: at 4hp per minute, after 30 minutes you would receive 120 hp damage (4×30= 120)
      Frigid: at 2hp per minute, after 60 minutes you would receive 120 hp damage (2×60 = 120)
      Cold: at 1hp per minute, after 2 hours (120 minutes) you would receive 120 hp damage (1×120 = 120)

      If he failed his CON save and received maximum damage each minute, the minimum time he would survive is one third the minimum time indicated on your table:
      Icy: at 24hp per minute, after 5 minutes you would receive 120 hp damage (24×5= 120)
      Frigid: at 12hp per minute, after 10 minutes you would receive 120 hp damage (12×10 = 120)
      Cold: at 6hp per minute, after 20 minutes you would receive 120 hp damage (6×20 = 120)

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