Moringa seeds can be effective in the treatment of water because they contain a cationic electrolyte. They can then replace the sulfate of alumina or other flocculants. In this study, we opted for the clarification of surface water from the river M'Poko using seeds of Moringa oleifera dried and transformed into powder. In the literature, we can find very different quantities of seeds used. We have used a method of experimental design to optimize the treatment of our samples of raw water with the seeds of Moringa. The experimental design used is a full factorial design that determines the importance of various factors and also the relationship between these factors so as to identify the best conditions to meet the target set by this study, which is to clarify a maximum quantity of raw water from the river. Another problem, met in the use of Moringa, is the important contribution of organic matter in the water treated by this natural coagulant. To avoid a bacterial proliferation, in time, in the water so treated, we used sand/coal filtration, which proved to be very effective. The water, treated by Moringa and filtered, possesses turbidity and a quantity of organic matter corresponding to the required standards. Such water can thus, be disinfected by chlorination for human consumption. (c) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.