The demand for flush toilets rose sharply between the mid-1950s to the early 1970s. In 1960, a Japanese Industrial Standard for determining the capacity of Johkasou was stipulated. In 1969 when the Structural Standards for Johkasou was enacted, there was an equal number of users of sewerage systems and Johkasou systems. The Johkasou system became an effective measure to promote flush toilets as a sewerage system going into the 1980s.

Small scale Gappei-Shori Johkasou was developed in the 1970s and later became a commercial product thanks to the Johksou manufacturers. Now, it has become possible to treat domestic wastewater from individual households and multiple dwelling houses using Johkasou.

• Small scale Johkasou can be installed on a household level to treat and discharge wastewater locally. These provide local aquatic environment protection and cost-benefit advantages compared to sewerage systems.
• Johkasou-treated water and sludge are easy to reuse as Johkasou are designed to treat domestic wastewater from individual houses; there are few toxic substances in Johkasou-treated water and sludge. This makes it possible to reuse these for various purposes.
• A Johkasou can be installed in a small, unused space and requires no complicated procedures or cost.
• Small-scale Johkasou can be installed in a small, spare space and the device’s inflow pipes are short. Therefore there are very few topographic limitations when it comes to its installation.
• It takes only a week for a typical installation. Moreover, when the Johkasou begins functioning, its effect on wastewater treatment will be evident immediately.