It's just the word shower translated into ninja. They usually use wah-tah to take their shao-waahs!
Boy: Hey ninja!
Boy: Do you take showers?
Ninja: If you mean shoa-waahs! Then yes! I take shao-waahs, and I like to use wah-tah!
The all-natural beverage that ninjas indulge themselves in on a daiy basis. It is also used in the cleansing ritual Shao-waah.
Boy 1. What do Ninja's drink?
Boy 2. Wah-Tah!!