eh i mean as long as its ipx4 it should be fine in a rainstorm the only issue would be if you accidentally leave it in a backpack with a leaky water bottle (have lost a few phones to that and now I get waterproof phones haha)
Why would you subject your headlamp to that much water? If your going to swim with it than they make headlamps purposely for under water. There is no need to make them fully waterproof that is unnecessary
