Playing through Wario Land 2 again, I can't help but wonder...

[KingDragonWario]

Why in the world does Wario have a giant faucet installed in his castle?

 

[Crescent-Moon Villager]

To fill a really big bathtub?

 

[Just a Wario Fan]

For the same reason Princess Peach's castle is filled to the brim with stairs, long hallways and pictures that don't make any sense at all: because it's a video game and all these random things are just there for the sake of the plot.

Canonically: maybe Wario had indeed a really big bathtub once there, and enjoyed swimming in it.

 

[Handsome Count Cannoli]

Because he is rich and eccentric?
If i had so much money i would probably install an giant washing machine that is a gallery that is filled with nothing but portraits of Tom Selleck.

 

[Yikes Spike]

I think that's how his water tank works.

 

[The 3rd Wario Brother]

To get the tough stains out

 

[ShyGuyXXL]

It's just a really stylized shower.