The injection rate of PAC is typically around 20-40 mg/L, and the ALT ratio (aluminum injection amount mg/L) / (turbidity mg/L) is considered standard at around 0.05-0.2. However, when the raw water contamination progresses, the sedimentation of suspended solids deteriorates significantly, and there are cases where over 100 mg/L is injected. This can be considered a state where it is being used more as an adsorbent than a coagulant, so in such cases, the introduction of advanced treatment should be considered urgently. A small amount was used for testing.