OK, let's see here...
POSSIBLE SECONDARY TYPE OPTIONS FOR WATER
(since Water will probably win anyway)
Current Problems:
Zapdos
Pyroak
MAYBE Strategem w/ Giga Drain + Tech
(if we make it slow and not access Aqua Jet)
Mono-Water: No, just no... we've got WAY TOO MANY mono-waters, we don't need another one.
Water/Normal: Revvy checks in, no-one checks out. End of...
Water/Fire: Makes Strategem even worse, and allows Fidgit and TTar to jump in on the fray. Syclant and Heatran MAY also come in and KO w/ Earth Power. Bad trade off for Grass coverage IMO, and doesn't help against Zapdos
Water/Electric: Gets rid of Zapdos, but allows Syclant and possible Fidgit/TTar/Heatran entry and. Also Lanturn territory, albeit it doesn't do too well at its job IMO
Water/Grass: Better defences against Pyroak, but doesn't phaze Zapdos. Fidgit MAY come in, but only if it has Sludge Bomb, which isn't likely. Scylant and Scizor can also come in. Currently Ludicolo territory
Water/Ice: Scares Zapdos a bit, but in return for Revvy, TTar and Scizor jumping in, and Building Gem's confidence? Not worth it, at all
Water/Fighting: Does nothing to help scare off Pyroak and Zapdos, but it does intimidate Blissey, with no more weaknesses in return. Overall, not bad in terms of helping decentralization, if we can get around Poliwrath territory
Water/Poison: Pyroak's no longer a problem, but Stratagem can now resort to Earth Power if need be. Scylant comes in for the kill though, as do Fidgit, TTar and Heatran if they're feeling brave enough. Tentacreul territory is worth a mention
Water/Ground: Zapdos is no longer a counter, but Strategem and Pyroak are well rewarded for sticking around. Swampert territory is worth a mention too
Water/Flying: Zapdos fodder. Also allows couragous TTar's to come in. On the plus side, it does get rid of Pyroak. Gyarados is in the domain ATM
Water/Psychic: Revvy and TTar might come in. Scylant and Scizor DO come in. Overall, worse than Water/Normal
Water/Bug: See Water/Flying. Surskit's not viable, which means that Water/Bug is technically free
Water/Rock: Well it does scare both Zapdos AND Pyroak, but they MAYBE still willing to stick around, the latter being well rewarded for doing so. Same with Strategem. Revvy and Scizor come in too. Add Omastar and Kabutops and Relicanth territory in the mix, and you've got an iffy combo on your hands
Water/Ghost: Revvy and TTar might come in. Doesn't help with Zappy and Oaky either. Not good
Water/Dragon: Zappy and Oaky check out, nothing checks in. On the other hand, Kingdra territory will probably be a bitch to get around. Apart from that, it'll probably be the best bet
Water/Dark: Easily the worst combo of the lot, as Revvy, Scylant and Scizor come in for free and no-one will be willing to back down.
Water/Steel: First off, Empoleon territory. Secondly, Revvy comes in confidently, and Fidgit, TTar and Heatran may come in. Does get rid of Pyroak though, but is it really worth it?
On a side note, I should point out that Heatran DOES have Earth Power and DOES use it.