A note on SureFire & 'waterproofness'
SureFires are rated as "weatherproof".
Many SureFire are designed, manufactured and assembled to be capable of being tested and rated waterproof to 30 metres.
However, if SureFire considers a product to be waterproof it will be clearly identified as such (including a depth rating).
TailCaps and other threaded components should screwed on tight and should not be rotated underwater. Note that double o-rings improve the ability of a threaded component to be rotated underwater but it is still discouraged.
One of the most important factors regarding the effective ability of o-ring(s) to provide a water-tight seal is keeping the o-ring clean and correctly lubricated, undamaged and the surfaces it comes into contact with also clean. This is especially difficult if the o-ring is exposed by unscrewing threaded components, or even rotating them. As a result SureFire can not be responsible for the waterproofness of seals that have been exposed (for example a TailCap that has been removed to replace the batteries). It is for the user to ensure that sufficient care and attention is given to the ongoing ability of the seals to perform as required.
I suggest that any threaded component that is regularly rotated and o-ring seals exposed, and it carried in a pocket and/or subjected to a dusty (etc) life is not going to be as suitable for underwater use as a dedicated divelight.
To that end I would not expect my EDC - an L2 to be waterproof without cleaning and likely replacing the o-ring before taking it underwater constant-on. If my use or role required me and whatever I'm carrying to spend regular time underwater I would select a different flashlight as my EDC.
Al