By checking out the most amazing site on the web, you can find helps against water attacks.

Absorb:
Behemoth Suit, Cat Hood, Gaia Gear, Genji Armor, Genji Helmet, Genji Shield, Imp's Armor, Moogle Suit, Nutkin Suit, Snow Muffler, Tabby Suit, Titanium, Tortoise Shield

No Damage:
Paladin Shield

Half Damage:
Force Armor, Force Shield, Minerva

After looking over the list, it looks like a party of imps could have a good time against Leviathan. :mog: