Suffocation

When you lack air, you lose 1 FP per second.
At 0 FP you must make a Will roll every second or fall unconscious.
After 0 FP you start losing HP instead, as per usual.
Regardless of FP or HP, you die after 4 minutes without air.

Drowning
When you are drowning after a failed Swimming roll.
You can get some air but also inhale water, roll against Swimming every 5 seconds, failure costs 1 FP.