Heterotrophic Bacteria Count Index in Drinking Water and Possibility of Biofilm Formation in Household Drinking Water Treatment Devices in Sari, Iran

 Background and purpose: Household drinking water treatment devices are becoming commonplace to improve the quality of drinking water, remove odor, taste, turbidity and color, pathogenic organisms, toxic chemicals, organic matter, and carcinogenic pollutants. This study aimed at investigating the Heterotrophic plate count (HPC) in drinking water and possibility of biofilm formation in household drinking water treatment devices in sari, Iran. Materials and methods: In a descriptive-analytical study, 100 samples were collected from the inlet and outlet reservoirs of urban drinking water distribution network and household water treatment systems according to the standard method in summer 2019. HPC culture was tested by spread plate method using R2A agar culture. Results: Among the samples studied, HPC was 12% higher than the standard level in 25% of urban water samples and 4% higher than the standard level in 18% of home water treatment system samples. Low residual chlorine in network and effluent of treatment devices and presence of heterotrophic bacteria in these samples, reinforces the possibility of biofilm growth on the network system and devices. The study showed significant relationship between lifetime of the filters, HPC, and residual chlorine (P<0.001). Conclusion: Presence of HPC in network and effluent samples of household drinking water treatment devices and low residual chlorine in samples increases the rate of biofilm formation in network and devices even by small amounts.