When preforming this move, Squirtle shoots water. It is functionally similar to Mario's F.L.U.D.D. in that it utilizes water, requires a charge, and has only pushforce, although it charges faster than F.L.U.D.D. and has more pushforce and range (the latter untrue when uncharged). If the player starts charging the move in the air, Squirtle is able to move left or right while charging. In Brawl, if Squirtle is recalled, its charge will be lost. The player may also change the full spray's direction by tilting up or down. When fully charged, Squirtle can hold the charge and battle normally until the player presses the special button again.
In Brawl, when used uncharged, it does a short ranged attack that deals about 12% damage with minimal knockback. In Ultimate, it acts like all other levels.
A fully charged Water Gun can be performed on an opponent who is in his/her helpless animation trying to grab the ledge (this can also work with Mr. Game and Watch, Snake, R.O.B., Pit, Sonic, and Peach after they have used their third jump). Doing so will push them away from the ledge. Also, it is possible to push Ness or Lucas away from their PK Thunders (though it is possible that the opponent can move their Thunders back to themselves quick enough). Finally, the player can use Water Gun on an opponent that is swinging a Hammer. Since players cannot use midair jumps and/or up specials while holding one, they would most likely be KO'd. All of these techniques can be used by Mario's F.L.U.D.D.
An aqua jump occurs when Mario's F.L.U.D.D. or Squirtle's Water Gun hits any jumping character just before they begin to lose momentum. This causes the jump to rapidly speed up and double in height. It is technically not so much of a technique as a misuse of the two aforementioned moves.
In the Pokémon universe, Water Gun is a special Water-type attack which is a common attack for most first level Water-type Pokémon, Squirtle included. As it is learned at an early level, it is rather weak, and stronger Water-type attacks can replace it.