Backgrounds and Aims: Human health depends more than anything else to clean water and sanitation, thus safety of drinking water is one of the most important community health aspects. The objective of this study was determining microbial quality trend of drinking water in rural area of Kermanshah during 2004-2013.

Material and Methods: This was a descriptive–analytical study. Ten years references laboratory data from Kermanshah Health Center were obtained.  Total coliform, termotolerant coliform and residual chlorine of drinking water samples have been analyzed statistically using SPSS Ver.16.and Excel software.

Results: Base on water quality assessment of Kermanshah, the microbial contamination percent of villages covered by ABFAR decreased from 44% in 2004 to 20% in 2013, whereas in noncovered villages decreased from 70% to 47% during the same time. Contamination rate was lower than the summer time during the winter time. Free chlorine residual testing of drinking water among all studied area improved from 33% to 75% during ten years period.

Conclusion: During last ten years, microbial contamination has been decreased more rapidly in covered villages than non-covered. However, there is still a long distance from the ideal situation. Based on the WHO recommendations on evaluation of microbial safety of drinking water, the average desirable of the bacteriological quality of drinking water in the villages covered by ABFAR in the ten-year period was determined well in winter and bad in summer. These conditions for non-covered villages, was determined moderate in winter and bad in summer. According to chlorination role in water safety, restrict supervision is necessary to provide public health.