Residual aluminum control for source water with high risk of overproof coagulant residue: A novel application of principal component analysis

•Focus on Al residue in full-scale clarifiers-Densadeg and mechanical clarifier (MC).•First application of the PCA and MLRA to estimate the level of aluminum residue.•Good prediction of Al residue by Fe dose, water temp. and turbidity for Densadeg.•Well predicting Al residue by Fe&PAC dose, water temp., turbidity and NOM for MC.•A low cost method for effective Al residue control in water plants in developing countries.