The effect of iron corrosion in cast iron pipes on the microbiological quality of drinking water: a laboratory and field investigation

Iron pipelines are commonly used in old drinking water distribution systems, adding rust to pipe-borne water. Chlorine added to water for disinfection could react with iron that leaches from these iron pipelines, thereby reducing available free chlorine for disinfection. The consumption of dissolved chlorine by iron and consequent effects on the microbiological quality of drinking water were investigated, by spiking Serratia marcescens and Escherichia coli into different known mixtures of Fe²⁺ and chlorine. Twenty seven water samples were collected from three water supply systems at the University of Peradeniya, Sri Lanka and investigated for its iron content, residual chlorine and microbial quality. The selected water distribution system is 60 years old and is corroded to a large extent, adding rust to the pipe-bone water. The results indicated that the rate of chlorine consumption in water was directly proportional to the content of Fe²⁺ ion in water. The Fe²⁺ concentration in drinking water in iron pipelines ranged from <0.01 to 0.64 mg/L, while the desired residual chlorine levels were not obtained. Both total and fecal coliforms were detected in some samples indicating that the disinfection was not effective due to chlorine consumption in the distribution system. It was also observed that a high level of ferrous ions in water was inhibitory to microorganisms by forming iron-bacteria clumps in water.