Most water supply systems in developing countries incorporate storage tanks. The principal advantages of storage include the fact that it equalizes demands on supply sources, production works, and transmission and distribution mains. These tanks, however, may have an adverse effect on the water quality, which can deteriorate dramatically from point to point in a network. Also, as water moves toward the periphery of a system, the residual disinfectant disappears. The water quality deterioration includes the increase of water age, reduced disinfectant residuals, and enhancement of microbial and algal growth. Soroti town, North of Uganda, is selected to be assessed and to identify the impact of its storage tanks of 2100 m3 on the water quality. The samples has been collected and analyzed over two years from 13 stations along the water supply system. Several statistical analyses are conducted to define the significant difference between the water quality of different points along water supply system. The analysis includes, test normality, whisker box plot, cluster trees analysis and ANOVA test. Finally, decay rates of residual chlorine are estimated using first order linear decay formula. Results indicated that water quality is degraded as a result of long residence times in storage tanks which can reach 25 hours, where the fringes are the most impacted location. A cluster analysis conducted using the Ward’s method with Euclidean distance show that the junctions can be divided into three to four clusters where the tank itself a cluster. The estimated chlorine decay rates of the storage tanks vary between 0.30 to 0.55 day-1. It is clear that over design of storage facilities should be avoided. Providing redundant storage leads to decreased volumetric change and increased water age. Consideration should also be given to take excess storage facilities off line during periods of low flow. |
