If you visit Japan, you will find that they have very different bathing customs than we do in the West. When you take a bath in Japan, you wash yourself in a separate area and rinse off the soap before you get into the Japanese bathtub or Japenese bath shower. There are three different types of Japanese bath tubs that you may encounter in a trip to Japan. In each of these types, the water is not changed between uses, as the water does not get dirty like it does in traditional Western baths. Before using a Japanese bathtub, you must wash up and rinse yourself thoroughly before you climb into the tub.
The first type of Japanese bathtub that you may encounter would be a small square wooden tub usually found in private homes. Though the Japanese bathtub is shorter in length than a Western style bathtub, the tub is deeper. The shape of the tub is designed so the bather sits with their knees against their chest, but the water comes up to shoulder height, allowing the bather to soak their whole body in the warm water. These types of Japanese soak tubs are covered when not in use to keep the water from evaporating. Additionally, because the bathers wash before they get in the bath water, the water is not drained between bathers. Instead, each family member will soak in the Japanese bathtub, using the same water each time. If the tub is large enough, parents will bathe with their babies, toddlers, and young children.
The second type of Japanese bathtub that you may encounter would be a Sento. This is a communal type of Japanese bath, with a small partition separating the areas for men from the areas for women. Each bather will change and wash in an area designated for washing. After the soap is rinsed off, the bather will get into the communal tub unclothed, though occasionally a washcloth is used to cover the genitals. Though many homes are now being equipped with a private Japanese bathtub, communal bath houses are still used. Many times, a Sento is used for socializing, or some houses are not large enough to have their own private tub. In a Sento, the water is heated with a boiler or furnace. With the increase in the number of Japanese bath tubs in private homes, the number of Sento bath houses has been in decline.
The third type of Japanese bathtub is a subset of the second type. An Onsen is a Japanese bath where the water comes from hot springs. Typically, the Japanese have felt that hot springs are good for the health and healing. Because of this, the Onsen bath houses are not experiencing the decline seen in Sento bath houses. Additionally, Onsen bath houses are generally built outdoors, with either open air tubs or a view out the windows. Especially in rural areas of Japan, Onsen bath houses are not segregated by sex because of tradition. It was only since Japan was opened to the West that the Japanese bathrooms started segregating for the sexes.