The most common and wide spread health risk associated with drinking water is microbial contamination. The aim of this study is to assess microbial contamination of drinking water, starting from source to distribution systems. Water samples from the Arba Minch town of Southern Ethiopia were collected randomly from the main source before chlorination, reservoir after chlorination and from different points of distribution lines. Total coliforms, fecal coliforms and heterotrophic plate count (HPC) were determined from collected water samples. Coliforms were analyzed by using the most probable number (MPN) method. About 93.3% of collected water samples were contaminated with total coliforms and 16.7% of distributed tap water was contaminated with fecal coliforms. Most of the analyzed water samples had high number of viable bacteria or HPC (>5 log), and total coliforms. The HPC ranged from 1.9 log of bacteria in the chlorinated water in reservoir tank to 8.44 log in the source water before chlorination. Overall, the quality of drinking water suggests that the distribution lines are the most likely point of microbial contamination. Therefore, regular bacteriological monitoring and maintaining residual chlorine in distribution system is mandatory.
Key words: Coliforms, drinking water, heterotrophic plate count, microbiological point of contamination.
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