>>17879617By water team, do you mean all water, or just mostly water? Also, singles or doubles?
Politoed is a must, damp rock could be useful for it. Dual-Types are important; Lanturn and Gastrodon both offer good resistances. Smogmachine is pretty much king of OU in Smogon tiers, although very predictable.
If you're not a water monotype, Eelektross is a good idea. OK stats, and not weak to any type so long as its levitate is active. It's a sea creature any way, so it would match the theme.