At its simplest level, drinking water treatment seeks to remove turbidity (solids) and pathogens. Additional treatment may be applied to deal with specific problems, e.g. hardness and chemical contamination. The description of drinking water treatment which follows addresses the turbidity and pathogen issues and includes five steps: coagulation, flocculation, sedimentation, filtration and disinfection. Each of these terms will be defined and described in the following pages.