In order to enhance water quality, water quality standards have been set on seas, rivers, lakes and groundwater. Wastewater from factories and businesses are under regulation, and effluent limits has been set on biological oxygen demand (BOD), chemical oxygen demand (COD), nitrogen, phosphorus, among others. Regular monitoring on water quality is carried out by local governments.
Past regulations have been quite effective in improving quality of river waters. The average BOD in river water in Japan has dropped from 3.3 in FY1979 to 1.6 in FY2003. The main causes are considered to be improvements in water treatment in major factories and dissemination of sewage systems and “Joukasou” a Japanese system for household wastewater treatment.
On the other hand, improvements in lake water quality have been rather limited. Because of this, the government of Japan has been discussing policies to further improve the lake water quality by measures such as improving use of fertilizers and conserving lakeside vegetation.