There are mixed water supply zones between different water plants in multi-source water supply areas

where the hydraulic water quality conditions are not stable

and water quality problems such as excessive iron release and low residual chlorine are easy to occur. The mixed water quality risk area can be predicted by using the spatial modified interpolation method of characteristic water quality index. Characteristic water quality index refers to the index with distinct identifying characteristics

which are distributed regularly in the water distribution system and have large differences in the finished water of different water plants. According to its spatial distribution

the separate water supply area and mixed water supply area of each water plant can be determined. However

there are great differences between the distribution of pipe network and the geographical space

so the correction coefficient should be introduced before interpolation to correct the characteristic index. In this study

the mixed water supply zone of H city was predicted. Results show that the spatial modified interpolation results of the characteristic water quality index conductivity and total iron concentration of H city were basically consistent

and accorded with the results of hydraulic model simulation. Online monitoring points were set in the predicted mixed water supply zone

and frequent changes in flow velocity and flow direction were observed

which conformed to the hydraulic characteristics of the mixed water supply zone. It indicates that the prediction results are correct and the method is feasible.