I think of: (very inspired by HARP)
Starvation & thirst- by day without meal: - 5 to the total of exhaustion points
- by day without water: - 5 to the total of exhaustion points
These points can be recovered only with water and a good meal.
Thus a character with 90 in Co (90 exhaustion points) after 1 day without meal and water will be with 80 exhaustion.
When the sum of exhaustion points will at 0 the character will be coma state and He'll be dead in 1D10+Co bonus in hours.
SwimmingThe speed of the movement his at half the base movement of the character.
For the difficulty of swimming, see the table 07-07 page 81 of Character Law.
For current:- light stream: add one difficulty (thus very hard for Soft Leather or impossible in Plate...)
- strong stream: add two difficulties
- very strong: add three difficulties
Hold his breathHolding his breath is very tiring: a character lost 2 exhaustion points per round without moving. If the character want moving use the "rough terrain" thus x2 exhaustion points.
With the head under water, a character with 0 exhaustion point will be in a coma state and will die in 1D10 rounds.
One example: a character with 90 Co can stay under water (without moving) 45 rounds (90 exhaustion points /2 points per round;450 seconds or 7.5 minutes). If he moves on, the time will be 22,5 rounds (3.75 minutes...).
Heat & Colda) Heat
Use the exhaustion rules but over 130? F the character will take a A Heat Critical all the 10 minutes (B with metal armour).
If the character is wearing heavy clothes or armours change the category by one: at temperature 120?F with an armour the character will be at 130?F for the effects of the temperatures...
b) Cold
Use the exhaustion rules but under -50?F the character will take a A Cold Critical (B with metal armour) all the 10 minutes. With heavy clothes the category of cold will be one level up (for example if the temperature is -50?F a character with heavy clothes will be in the -30?F category).
Excuse me for my low ranks in the English langage...