Suspended particles in treated water can gradually accumulate in distribution pipes, which cause water discolouration after resuspension due to hydraulic disturbance. This study aimed to estimate the target concentration of suspended particles in treated water from the viewpoint of controlling such discolouration. We investigated the detachment process of accumulated matters triggered by the hydraulic disturbance in a pipe loop facility, and then developed a simple numerical model of detachment. A visual testing of drinking water was also conducted to determine the turbidity threshold at which customers start to perceive the cloudiness or start to complain to water utilities about it. Based on these data, the increase of turbidity during disturbance was simulated in the target network based on the amount of accumulation previously predicted. Then, the discolouration potential score, a new indicator of the possibility of discolouration incorporating the customers' acceptance, was calculated based on the estimated turbidity. The result showed that there were no pipes exceeding the acceptable score at the current concentration of suspended particles (10 μg/L) in treated water. However, pipes with unacceptable score appeared at the concentration of approx. 17 μg/L, which can be considered as a target concentration for controlling the discolouration.