The appropriate type of reclaimed wastewater reuse system in each area of Tokyo was evaluated from the aspect of economic efficiency, using a GIS-based water balances model. The following four reclaimed wastewater reuse systems and conventional waterworks and sewerage system were evaluated; “Rain water storage and use system”, “Onsite wastewater treatment and reuse system”, “Sewage treatment and reuse at an intermediate point on the sewer pipe” and “Treated water supply system in sewage treatment plant”. In the case that we install them to office and residential buildings, the supplied volume by reclaimed wastewater reuse systems is 693 thousands m3/d, this corresponds to 15% of total water demand in the area. Furthermore, the effects of the following scenarios brought about by technological innovation in water treatment were investigated; the case that flush water in toilet and wastewater from kitchen are also available as source in a “onsite wastewater treatment and reuse system” and the casethat reclaimed water is used for laundering in residential buildings. When reclaimed water is used for laundering in residential buildings, the supplied volume by these systems increases to 814 thousand m3/d in the case that these systems are installed to office and residential buildings.

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