Water is an attack type in the Super Smash Bros. series that encompasses water-based attacks. Water-type attacks (but not attacks with a water effect) are boosted by Water Attack stickers in Super Smash Bros. Brawl's The Subspace Emissary.
In Super Smash Bros. 4, the water type is unused; the only characters that might use it - Greninja and Pac-Man's Fire Hydrant - instead have their attacks coded as being either Typeless or Sword. It is used again in Super Smash Bros. Ultimate, though it is unclear whether it has any gameplay properties, as spirit effects operate on the effect instead.
List of water (type) attacks