Backgrounds & Objectives: In water quality analyzi heterotrophic plate count (HPC) has been used sufficiently as a supplementary indicator for monitoring of water quality in reservoirs and distribution systems. The maximum number of HPC is determined 500 CFU/ml by USEPA. Whereas the HPC does not use as a routine technique in monitoring of water quality, and because of not being published data from it in Ardabil city, this study was performed on water distribution system of Ardabil city in 2012.
Material & Methods: In this cross-sectional descriptive study, 42 samples from Ardabil distribution system were investigated. HPC, free residual chlorine, turbidity, pH and temperature were measured based on standard methods. Data were analyzed by regression test.
Results & Discussion: Out of 71% samples, examined by pour plate method using R2A agar culture media, showed heterotrophic bacteria. The number of colonies was more than 500 CFU/ml in 7% of samples. The mean of HPC amounts was 91±174CFU/ml for all samples, and the mean of free residual chlorine was 31±0.31 mg/l. Out of 40% samples had free residual chlorine less than 0.2 mg/l. This parameter was 0.0 in 18% of samples. There was statistically significant relationship between the HPC and free residual chlorine (p=0.039, R=-0.320), also between HPC and turbidity (p=0.00, R=0.647).
Conclusion: This study showed that because of presence of heterotrophic bacteria in 70% of samples, being free residual chlorine under guideline amounts in 40% of samples and the statistically significant relationship between them, getting sufficient free residual chlorine in water distribution systems is so important. In addition, periodic monitoring of heterotrophic bacteria as a supplementary indicator, along with the conventional microbial indicators such as total and fecal coliform bacteria must be considered. This may help to recognizing the problems in water distribution system and also show the water quality situation more clea
