Assessing the effects of Installation and maintenance of storage tanks on water quality in indirect domestic water supply systems

Abstract

Water supply systems form one of the most fundamental components of building services. In many communities especially in developing countries such as Uganda, most households use the indirect cold water supply system, particularly because of intermittent water supply problems. However, research has linked the main component of this system; water storage in form of overhead tanks, to contamination of water. This study investigated the effects of construction and maintenance practices of water storage tanks under the indirect domestic water supply systems on household water quality, to understand their contributions towards water contamination, and to guide decision making on the selection of features of water storage tanks during the construction and maintenance of the indirect water supply system. A total of 190 water samples were collected from 50 household water storage tanks and analysed for both microbial and physiochemical contamination. The results revealed that the treated water received by households became significantly (α=0.05) contaminated with faecal coliforms (p=0.001), total coliforms (p<0.001), heterotrophic bacteria (p<0.001) while in storage tanks. However, no E. coli was detected in all the water samples from the storage tanks. Furthermore, Fe, Mn, and colour significantly increased in storage tanks while SO42- and residual free chlorine significantly reduced. This study revealed that the type/material of tanks and tank connectors selected during the construction of the indirect domestic water supply system significantly affected water quality. Tank size was also found to affect water quality through retention time of water in the tanks, though the effect was not statistically significant. Surprisingly, tank cleaning was found to lead to contamination of water in the storage tank. This phenomenon is most likely to be attributed the unhygienic cleaning methods used by the households, and the positioning/lack of washout pipes that do not facilitate total emptying/ washout of the dirt and contaminates from the tanks during cleaning. This study suggests that when the tank features are collectively considered, tank type/material is the biggest predictor of water quality under the indirect domestic cold water supply system; and tank cleaning does not guarantee improvement of water quality in the tanks.