The Water-type has always stood out as a solid, reliable type in Pokemon battling. Matchup-wise, it's very much so, as it only has two defensive weaknesses in Grass and Electric, both of which are very exploitable, and it checks out very strong types such as Fire and Ground offensively. No particular stat stands out with Water-type Pokemon; they come in all shapes and sizes.
All of these qualities make Water-type a very capable one on its own, and the Pokemon on this list have proven that. Despite their singular typing (or maybe because of it), these Pokemon have made waves in the metagame over the years.
10 Politoed
Once the premier rain-setter, Politoed can still play that role decently well. Its Drizzle ability was an asset on many a rain team, as it was once the only fully-evolved Pokemon to have it as an ability besides Kyogre.
That's changed, as Pelipper gained the ability in Generation VII and swiftly overtook Politoed as the best in that role. Politoed is still a fine choice if rain is needed, but Pelipper is honestly a better one considering it's much more offensively capable with its superior learnset and stats. Same can be said for its other potential role as a Water Absorb pivot, with Quagsire and Dracovish currently filling that need better.
9 Pyukumuku
For a Pokemon whose only way of damage is Toxic stalling, it's seen some occasional use in the higher tiers of competitive battling. It's garnered a reputation as one of the most annoying Pokemon to battle, and it's perfect for opposing players that are too impatient or flustered by its ability to just stay on the field and do nothing.
While its signature ability Innards Out can be good for some last resort damage, its other ability, Unaware, improves its defensive capabilities by not accounting for the opponent's stat changes. That works in tandem with its most common sets that contain moves such as Block, Spite, Recover, and Toxic for stalling its opponent away.
8 Feraligatr
The Sheer Force ability has brought the best out of otherwise middling Pokemon, and it's done especially so for Johto's Water-type starter, who has it as a hidden ability. Sheer Force removes attacking moves' secondary effects, but boosts their damage output.
Feraligatr in particular puts that ability to use with moves like Liquidation, Crunch, Ice Punch, and Rock Slide. It wouldn't hurt to boost its offensive capabilities further with set-up moves like Dragon Dance or Agility, as it's got pretty good bulk on the physical side. Aside from the aforementioned Sheer Force-boosted moves, it's got a surprising bunch of other coverage moves, too, like Outrage, Shadow Claw, and Earthquake.
7 Vaporeon
Vaporeon is one of the first three Eeveelutions, and it's arguably been the best of the three for a while. It's got the highest HP out of all the Eeveelutions at 130, which has given it a decent role as a defensive Pokemon.
While it doesn't have a lot of attacking moves, mainly relying on STAB moves like Scald and Flip Turn and not having access to a lot of coverage moves; it's got a bunch of utility moves in its arsenal, such as Toxic, Heal Bell, Wish, Roar, and Protect. It also, like Politoed, has access to Water Absorb, which gives Vaporeon excellent pivot potential.
6 Blastoise
It's never dominated the metagame, but Blastoise has always been a suitable niche choice for teams. It's somewhat of a jack-of-all-trades stat-wise, but its best asset is its bulk, at 100 Defense and 105 Special Defense. Move-wise, it's got strong STAB options like Surf, Scald, and Hydro Pump, and utility moves like Toxic, Rapid Spin, and Flip Turn.
It received a Mega Evolution in Generation VI, which upped its viability a bit by giving it a role as a special wallbreaker, with a huge spike in Special Attack and the Mega Launcher ability. It lost that in Generation VIII, but got access to Shell Smash as a consolation, allowing it to still be an offensive threat if needed.
5 Milotic
Another particularly bulky Water-type, Milotic was perhaps the best of that bunch, at least of the pure-typed variety. Its 95 HP and 125 Special Defense make it very difficult to kill, and there are many ways to preserve that bulk further.
It helps that one of its abilities, Marvel Scale, boosts its Defense when inflicted with a status. Alongside usual suspects Toxic and STAB moves Flip Turn and Scald, it also has access to some of the best moves for stalling, mainly Recover for instant HP and the especially rare Haze for eliminating opponents' stat boosts. It doesn't like seeing Electric- or Grass-types, but if you're prepared with checks for them, you're golden.
4 Manaphy
Arguably the most concerning Mythical absence in Generation VIII, Manaphy had been making a name for itself as one of the strongest special attackers around, even though its stats are 100 across the board.
What made it so deadly was its access to Tail Glow, which improved its Special Attack by a whopping three stages. That made it incredibly dangerous not just with STAB moves like Surf and Scald, but with important coverage moves like Psychic and Ice Beam. It's best on a rain team, boosting its Water-type attacks further and taking advantage of Hydration. Just one problem: Tail Glow hasn't returned to Sword and Shield either, so Manaphy's future viability might be up in the air.
3 Suicune
The Water-type Legendary beast has become one of the most infamous Substitute users in the metagame, as it has the capabilities to take hits, put up a Sub, and do what it wants from there.
Of course, it can do that due to its high Defenses and relatively low Speed. Once the Sub is up, it has a whole host of options. Its main post-Sub agenda is usually to set up with a few Calm Minds, then either stall the opponent out with some additional Pressure help and constant healing with Leftovers and Aqua Ring, or sweep the other team with STAB moves like Hydro Pump and Scald, and coverage moves like Ice Beam.
2 Barraskewda
Some Water-type Pokemon made their living out of being Swift Swim sweepers, i.e. taking advantage of the aforementioned ability's Speed boost in the rain to knock down their opponents. Thanks to Barraskewda, they're all out of work.
This relative youngblood from Generation VIII has dominated the metagame in that role, boasting the highest Speed stat out of all the Pokemon with Swift Swim at 136. It's also got a spectacular Attack stat at 123, as well as the necessary STAB and coverage moves to OHKO most opponents — even some its biggest supposed checks. It's got garbage bulk, but that doesn't even matter when it can kill its opponents before they even get a chance to deal damage.
1 Kyogre
It's the god of the seas in the Pokemon universe, so it's naturally going to be the strongest of Water-types at large, let alone pure Water-types.
Its signature move, Origin Pulse, is quite frightening, essentially being a somewhat stronger and more accurate Hydro Pump, boosted by both STAB and the rain brought on by its Drizzle ability. It also works well with Thunder, guaranteeing it to hit while raining, and Ice Beam, as usual, to check Grass-types. All of that, combined with an insane 150 Special Attack and 140 Special Defense secures its place in Smogon's Uber tier. This is all without even mentioning its Primal form, which dominated Ubers alongside Primal Groudon in Generations VI and VII.