I'll try to answer this question. I am not Japanese, but I have spent some time in Japan, and I love o-furo. In Japan, the water is not changed for each user. Since you enter the bath clean, the water is used for soaking, not for cleaning, so it does not really get dirty. And, more often than not, you are soaking with others--taking a bath is also a social event.

The bath is filled with hot water. As you get in, some of the water overflows onto the surrounding floor (hence the drain surrounding the bath). I think that helps clear the tub of any particles that float on the surface. That's one of my favorite parts of the bath--initially getting in and having the water slosh out! There is also some sort of purification/ filtration system in each bath. At our house, we would like to install an o-furo, but we are still researching how to do it correctly.

In Japan, there are also onsen--natural hot spring baths. At onsen, fresh, naturally hot water is continually flowing into and out of the bath

Here are a few images of a bath in a women's dorm at a Japanese college. The first is the changing room, the second is the bath itself, and the third are the washing stations. In the evening, the women congregated here, talked and socialized. It was a great way for me to connect with people.

TY Dianeth..I am very familiar with this set up having live in Japan now for 5yrs. When we return to the States we will be building our retirement home thus incorporating thie bathroom set up. I do allocated space for it in my floor plan area 10'X10' for the tub and the washing station and another 4'X7' for the dressing area...I just want to know the est cost and wanting to know where to resource the tub and the drainage etc...,