Analysis of public drinking water quality along water distribution systems in Addis Ababa City

Abstract

In this study, the impact of physical parameters and disinfection on the availability of bacteria in treated water delivered to Addis Ababa residents was assessed. Thirty-four water samples were purposively collected from different points and physico-chemical and bacteriological parameters were analyzed following standard methods. The results showed that all physico-chemical parameters analyzed were in the standard ranges of the World Health Organization (WHO) and Ethiopian National Standards (ENS) whereas residual chlorine (0.2–0.7 mg/l) were not within the limit set by WHO and ENS at a few sampling points. Regarding bacteriological parameters, significant number of coliforms (TC (3–299 CFU/100 ml) and FC (2–36 CFU/100 ml) and HPC (26–308 CFU/ml) were detected at all
sampling sites although residual chlorine was maintained. Moreover, HPC was significant positive correlation with TC (r = 0.934 at P value of 0.01 and r = 0.599, at P value of 0.05) and FC (r = 0.614 and a significant negative correlation with RCl (r = -0.620 at P value and r = -0.792 both at P value=0.01). On the other hand, TC and FC had a significant positive correlation with each other (r = 0.643 and r = 0.811 both at P =0.01) and significant negative correlation with RCl (r = -0.638 and r = -0.614) and (r = - 0.545 and r = -0.094), respectively. The study indicated that residual chlorine in some sample sites might not be efficient in killing microbes and there might be regrowth of microbes along the various distribution systems in the supply lines.

Keywords/phrases: Coliforms, Disinfection, Distribution systems, Drinking water, Residual chlorine