H2O coverage is only for US citizens. However it is worldwide in coverage.
The other major insurer is DEPP (
http://www.equipmentprotection.com).
There have been several discussions comparing the two, mostly over on the Camera/Housings board, but in short:
H2O pays out in cash, has a higher deductible, and does not cover for losses while the equipment is in your "care and control" (i.e., dropping while being handed off to you from the dive boat, washed overboard from the dive boat).
DEPP is a replacement/repair policy. You don't get cash, you get a replacement/repaired unit. Lower deductibles, basically will cover for anything. Have to cover for the F word separately. Used to require insuring at least a regulator and BC before you could cover for unintentional water exposure, but no longer.