Taken from Waterproof standards for VHF Radios - WTF is JIS / IPX?
The JIS Scale
The Japan Industrial Standards (JIS) for water resistance uses a "0" to "8" scale to define the level of water ingress protection built into VHF Radio. If the radio has been tested in compliance with this standard it is usually listed on the product spec sheet.
◦JIS "0" No special protection
◦JIS "1" Vertically dripping water shall have no harmful effect (Drip resistant 1)
◦JIS "2" Dripping water at an angle up to 15 degrees from vertical shall have no harmful effect (Drip resistant 2)
◦JIS "3" Falling rain at an angle up to 60 degrees from vertical shall have no harmful effect (Rain resistant)
◦JIS "4" Splashing water from any direction shall have no harmful effect (Splash resistant)
◦JIS "5" Direct jetting water from any direction shall have no harmful effect (Jet resistant)
◦JIS "6" Direct jetting water from any direction shall not enter the enclosure (Water tight)
◦JIS "7" Water shall not enter the enclosure when it is immersed in water under defined conditions (Immersion resistant)
◦JIS "8" The equipment is usable for continuous submersion in water under specified pressure (Submersible)
The IPX Rating
The IPX rating usually comes as IPX-7 or IPX-8.
•IPX-7 - water-proof, immersion resistant for 30 minutes under 1 meter (3 feet) of water.
•IPX-8 - water-tight under immersion for 30 minutes under 2.6 meters (8 feet) of water.
Not really surprising it didn't survive. Live and learn, I guess.