Tanaka ke, Tensei Suru. - Vol. 2 Ch. 10

[MangaDex]

 

[eng1]

They are the richest noble family and water is too expensive?

 

[Xe11o]

They are the richest noble family and water is too expensive?

I imagine it's rather that it's scarce and they prefer not to be wasteful. Might be a slight mistranslation of environmentally expensive to economically expensive.

 

[Tairo]

There wouldn't be running water, so someone would have to go fetch it by the bucket from either a well or river, and they wouldn't want to overwork their staff.
It's also not uncommon for Japanese families to not replacing bathwater between people, since they only sit in the tub to soak after getting clean, so that might also just be the family's habit.