The objective of the present work was to investigate the efficiency of two coagulants, aluminium sulphate and Moringa oleifera seeds, for clarifying water, and to understand the possible mechanisms involved in the coagulation process. Moringa oleifera is a tropical plant whose seeds contain a water-soluble protein which has excellent coagulation properties for treating water. Jar tests and measurements of electrophoretic mobility, in different dosages and pHs of the coagulants, were conducted. The results confirm the action of different mechanisms of aggregation for both coagulants, and the efficacy of using Moringa oleifera seeds for water clarification.