The scarcity of clean water is one of the main problems faced by big cities like Jakarta. With the density of population and office buildings, it is difficult to fulfill clean water. One of the difficulties in meeting the need for clean water is PT BM, which is a state-owned company that is building an area containing offices and residences for employees. The water requirement per day for the area is 370 m3/day, while the water supply available is from regional drinking water company only 100 m3/day. The deficiency of 270 m3/day of clean water can be met by reprocessing wastewater from office buildings and residential in the areas. The wastewater treatment system in this study uses a reverse osmosis system. The results of the research prove that the treated water of reverse osmosis can be used along with the water from drinking water company for building’s clean water.