In drinking water supplies systems, water from natural courses is fully treated before being supplied to a distribution system from where it will go to consumers. Water treatments consists in sequential units to eliminate pollutants and pathogens. It usually includes pretreatment; coagulation, flocculation and sedimentation; filtration and disinfection. Performance models can help in understanding and predicting treatments effectiveness, especially in stream events when abstraction water changes like during storms or droughts.