Wasserschlag usually refers to a phenomenon when water enters an engine's cylinder and jams it (called "hydrolock" in English), but here it literally means "Water Strike".
Had to take a little liberty with the EN translation to emphasize the "single blow" aspect of 一撃, since it's a set up for the next punch (heh) line.
ka‑SPLOOOOOGE
GLOWWWW
You, her—shrews, all of you!
Where did she come from?
fssh‑SCHHOTT
Aahh!
Springwater Slugshot—
WASSERSCHLAG!!
Written in Japanese as "Water Strike" (but the word for "strike" can be individually interpreted as "single blow"), given the German reading "Wasserschlag" (also "Water Strike")
Oh shaddap, Missus Discount-Bin Baddie.
Today is the day when I will no longer suffer this to pass!
You damned forest floozy!
Laying a hand on somebody else's devotee again!?