Raw water must be treated before public use to remove contaminants and make it safe. Treatment methods include screening, sedimentation, filtration, disinfection, and others depending on water quality. Sedimentation involves reducing flow velocity to allow suspended solids to settle. It can be aided by coagulation/flocculation. Horizontal sedimentation tanks are designed such that particles have sufficient time to settle out before exiting. Proper design of tank dimensions and overflow rates is needed to maximize removal of contaminants.