Study on a new index for yellow water problem during source water switch and its application on one real project

The evaluation of yellow water problem in drinking water distribution systems (DWDSs) by Larson ratio, Langlier saturation index is associated with fairly large uncertainty. As the background, one city in East China plans to change its water source from the local River A and River B into a new Lake C. Real servicing pipes were excavated in this city and assembled into 12 pipe section reactors (PSRs). The objectives of this study were to develop a more accurate index to predict the iron release in DWDSs, to verify the validity by simulation experiments with PSRs and to develop the reconditioning measures for the forthcoming source water switching project. A new index called iron stability index (ISI) was proposed by dividing alkalinity with the Larson ratio. Its validity was verified by the data in this study and literatures. ISI present closer linear relationship than that of LR and LSI in the situation where the concentration of anions (chloride and sulfate), and alkalinity in raw water and the switched water change more drastically. The water source switching from the local River A to the new Lake C was predicted not able to bring yellow water problem while that for the local River B to the Lake C has the risk. The water quality reconditioning measures were evaluated to address that concern and applied successfully in this project.