Rapid urbanization of the Philippines, especially of Metro Manila area, has caused serious water pollution. Main causes of this are categorized into industrial wastewater and domestic wastewater, discharged without sufficient treatment. As for industrial wastewater, it is essential to put strict regulations on effluent standards, and for municipalities to keep a regular check to ensure these regulations are observed. Philippine government has been working on the improvement of the legislation and control of industrial wastewater until now. However, from now on, it is vital to put more efforts in getting domestic wastewater treated properly. It is indeed crucial to put the existing sewerage construction plans into practice, but generally, sewerage systems require; 1) long construction period, 2) effective funding, 3) high-density construction, and 4) human resources to run the systems effectively. Meanwhile, on-site waste water treatment tanks, or what we called purifiers, can play an important role in controlling the pollution of water environment, and they will serve to complement the sewerage system even after the completion of construction. Small-scale on-site wastewater treatment tanks, or small-scale purifiers, developed and used in Japan especially in developing countries, not only in the scope of environmental conservation but also from the viewpoint of utilizing the economic resources in the private sector