Water Wave

Water Wave (ウォーターウェーブ) is Wave Man's special weapon. When used by Mega Man, it sends a few series of water spouts as a small wave across the floor. It will stop when it hits an enemy that is strong enough to sustain the hit, or until it hits a wall. It cannot be activated while Mega Man is in the air. It also can't be activated if Mega Man is at the very end of a ledge. However, it can be activated on a ledge provided it has time to flow off the edge where it will fall to the ground, and continue to travel until it hits something in it's path. It also negates Star Man's Star Crash.

Capacity
In Mega Man 5, one Water Wave uses 2 weapon energy units. With a full weapon energy gauge, Mega Man can use Water Wave 14 times.

Bosses weak against Water Wave

 * Mega Man 5: Star Man, Dark Man 1
 * Mega Man (Game Gear): Toad Man

Other media
Mega Man uses Water Wave in episode 13 of the Mega Man animated series. 

Trivia

 * Water Wave, Rush and Super Arrow are the only items affected by the gravity of Gravity Man's stage. While upside down, Mega Man is unable to use New Rush Coil and Rush Jet, he can't stand on Super Arrow, and the Water Wave only works if it is used at the time he touches the floor(or any terrain above Mega Man when he is on the ceiling).