the sharkman once bubbled...
...You also should replace the spring clips which are attached to the firing pin assembly. This piece should be replaced with the ones which are grooved for water. These are available only to Navy Seals (so I am told), but you can easily groove your own. Basically, I would not try it without switching/ grooving the spring clips....
Anyone now can get the special firing spring clips from any Glock parts supplier. Try "Top Glock". They cost $9 I think. My son bought some and I told him he better not use them. That they do is insure that the firing pin is not slowed down by the water. They do nothing to relieve pressure relative to the discharge.
Firing a Glock or any firearm underwater is foolish. Prior to politcal correctness I would say it was STUPID.
Dave D