The goal of this research was achieved to the general condition of bacteriological network of water supply in Hamadan city in 1371. For this purpose the network supply was divided into seven areas during eleven months, taking 1017 samples of water in these areas for the residual chlorine and bacteriological examinations. The results showed that 46.71% of the samples which were tested had residual chlorine up to 0.5 mg/lit, 6.29 had no chlorine and 47% of the tests were between 0-0.5 mg/lit.

Bacteriological examinations on the basis of Coliform search ia done in two probability and then confirmed tests. This examination showed that the Most Probable Number of Coliform in 100 ml (MPN/100 ml) for 4.03% of this samples were between 2.2 to 9.2. the most contaminated area was under cover of reservoir no.2 that located in Musala Hill.