Background and purpose: Safe drinking is water that does not have any chemical and microbial contamination. According to the World Health Organization (WHO) guideline standards for drinking water total and fecal coliform the indicator of fecal contamination must not be detectable in any 100 ml samples. Pollution indicator bacteria such as coliforms and fecal coliforms were enumerated using a multiple-tube fermentation method. Therefore, this study aimed to determine the microbial quality of domestic water wells in rural areas around Sari, Iran with most probable number (MPN) test. Materials and methods: In this cross-sectional study, the microbial quality of water samples from 23 domestic water wells in some villages of Sari were randomly tested in twice to determine the presence of total coliform (TC) and fecal coliform (FC) by the MPN. Sampling and sample transportation and sample analysis were done according to water and wastewater standard methods. Results: The results showed that 87 and 70% of the samples presented total and fecal coliforms, respectively. Water samples of 16 wells were bacteriologically nonpotable. Besides, the results showed that the bacteriological quality of the 3 wells was within the acceptable limits set by WHO guidelines and therefore was safe for human consumption. Conclusion: The results of the study suggested that the level of fecal contamination in domestic water wells was very high. The bacteriological quality of water was not according to the standard of WHO guidelines for drinking water. Therefore, using and drinking water from domestic water wells can pose a great threat and risk of waterborne epidemics by bacterial pathogens to the population consuming it. Water supplying authorities should consider this situation and take measures for the provision of contamination free drinking water to prevent waterborne disease outbreaks.

Keywords: Microbial contamination, groundwater, most probable number, Sari

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