With regards to the investigation into the relationship between pipeline material and the decrease in
residual chlorine, samples were taken from underground pipelines of various types that had been
constructed in different years. These pipes were filled with water (residual chlorine concentration
1.0-1.2mg/l, pH7.0). The changes over time in residual chlorine concentration and various water qualities
were measured. The results confirmed that the non-lining cast-iron pipe and the non-coated iron pipe
showed a trend of decreased residual chlorine.