Water for people.pdf - WHO Thailand Digital Repository

G R E A T E R T O KY O , J A P A N / 4 8 7Figure 22.1: Variation in river water quality – biological oxygen demand (BOD) levelsAnnual mean BOD (mg/litre)20 Tsurumigawa River (Ootsunabashi)Tamagawa River (Denentyofuzeki)Arakawa River (Sasamebashi)Sagamigawa River (Banyubashi)15Tonegawa River (Kurihashi)1050196519671969197119731975197719791981198319851987198919911993199519971999The BOD levels have decreased since the 1970s in all five rivers of Greater Tokyo. However, the level remains high in the Tsurumigawa and Arakawa Rivers.Source: River Bureau, MLIT, 2001a.Figure 22.2: Variation in the chemical oxygen demand (COD) discharge load by sector in Tokyo bayCOD (tons/day)50040030020047738115413408335536762863059OthersIndustrial effluentDomestic use2472852100324 250 243 197 16701979 1984 1989 1994 1999The majority of discharge load in Greater Tokyo is from domestic use, accounting for close to 70 percent of the total amount. The discharge load has drastically decreased, toabout half of what it was twenty years ago.Source: Ministry of the Environment, 2001.Most of the effluent load of four prefectures (Tokyo, Chiba,Saitama and Kanagawa) is emptied into Tokyo bay, where the CODlevel in 1999 reached 247 tons per day. Seventy percent of this loadis from domestic use (see figure 22.2). Due to drainage regulations,the discharge load has drastically decreased, to about half of what itwas twenty years ago (Ministry of the Environment, 2002).Groundwater resources are widely used in the region. One tenthof the water used to supply Tokyo metropolis is from groundwaterresources. Analyses of the water quality in 1998 show results lowerthan the standard values, except for tetrachloroethylene (a product