Which types combine well with water types in Pokémon? I have water types, so I need to know which types go well with them so I can make a good deck.
Check out the World Champion Decks to see which type synergies the top-ranked players are using
Regarding Water types specifically, the only Water decks released between 2004 and 2017 were:
- Pure-Water decks (x7)
- Water/Electric decks (x4)
Therefore, I think it's fair to say that Water and Electric go well together, possibly better than others.
Check out which type synergies are used in Theme Decks
You might also check out other Theme Decks that have been released to see other combinations that might go together. There isn't any guarantee that they'll be good, but presumably the deck synergies that are released will be functional, and types that work well together will probably get multiple releases.
For instance, there have been more Water/Electric and Water/Psychic decks released that Water/Fighting decks, and no Water/Darkness or Water/Fairy decks. Therefore, I'd infer that the former are probably more likely to go well together than the latter, since the Pokémon Company keeps producing decks with those synergies.
Rather than focus on types, the focus is generally on what your deck's archetype is.
The deck archetype is basically the main "goal" of the deck - if everything goes well, how are you going to be doing your damage and knocking out opponent's Pokémon?
Typically when constructing a deck, you have one Pokémon line or a few related Pokémon that are the "archetype". Then you have some "tech" Pokémon who exist for their ability and/or for some other purpose (they probably won't ever attack, and might not have the right kind of energy to attack), and you have some ancillary Pokémon that you use to support your archetype if it's not working well.
This is where Type synergy could come in: if you have, for example, a Metagross deck, you're weak to Fire, so you want to have (say) Ultra Necrozma, which is Dragon, as an ancillary attacker who can step in if the opponent is running a Volcanion (fire) deck.
You also could consider certain types as ancillary attackers who are super effective against particularly common Pokémon that you run into and have trouble handling (say, a Fighting Pokémon or two to handle Zoroark, or a Psychic to handle Buzzwole).
In general, though, you won't find all that many decks that actually run two energy types as co-equals, among strong decks. It's too important to have a single strong archetype most of the time.