The midstream of Blanakan is located between upstream and downstream. Due to its location, the water of midstream receives pollutants from nearby upstream. Hence, the purpose of this research is to investigate the concentration of Zn and coliform in the midstream. Coliform is one of the standards used for assessing water quality. The samples were collected from three stations in midstream. The Zn in water samples was analysed by using AAS. Meanwhile the coliform was examined by MPN and plate count methods. The results of obtained coliform then compared with the river water quality standards issued by Government Regulation No. 82 of 2001. In midstream of Blanakan, the ranges of coliform were 7.5 x 10^-1 MPN/ml, 9.3 x 10¹ MPN/ml and 4.3 x 10^-1 MPN/ ml. Meanwhile, the ranges of Zn contents were 0.45 mg/l, 1.53 mg/l and 0.5 mg/l. According to Government Regulation No. 82 of 2001, the limit of Zn is 0.05 mg/l and the limit for coliform is 10 MPN/ ml. To conclude, the Zn contents in water indicated that the midstream of Blanakan has been influenced by pollutants from domestic waste disposal from nearby upstream.

Blanakan, coliform, midstream, water, Zn