A study was carried out for the purpose of grasping the status of bacteriological contamination of the public wells in Iri city, during the period from 1 to 15 August, 1974. Coliform groups were detected by membrane filter method and physical conditions of the wells were checked. As results of this study, following conclusion were obtained. 1. The households which used the piped water occupied 70.8 per cent (11,907 households) out of total householdsir Iri city. 2. Temperature of the well water was 38 out of 50 samples (72.0%) with 12.1 to $16.0^{circ}C$ and 9 wells with 10.1 to $12.0^{circ}C$. 3. The pH values range of the well water was 6.0 to 7.9, 11 cases or 22,0 per cent less than 6.5 and 8 cases or 16.0 per cent more than 7.5. 4. The residual chlorine was found at 15 samples (30.0%) contained 0.1 to 0.5ppm, 9 samples (18.0%), 0.6 to 1.0 ppm after 24 houres of chlorination. 5. Coliform groups were found at 49 out of 50 samples (98.0%) before chlorination when 100ml well waters was tested by membrane filter technique and 15 wells(30.0%) were potable for drinking within 24 houres after chlorination. 6. Coliform groups positves were 23 out of 26 samples (88.5%) with no residual chlorine, 12 out of 16 samples (80.0%) with 0.1 to 0.5ppm and none out of 9 with 0.6 to 1.0ppm.