A method for treating water includes directing the water to a ballasted flocculation system and mixing a coagulant, flocculant and a ballast with the water. Solids are separated from a clarified effluent at a speed greater than 15 m/h. The method further includes filtering the clarified effluent with one or more microfiltration membranes or ultrafiltration membranes to produce filtered water. Thereafter directing the filtered water to an RO unit or a nanofiltration membrane or membranes and subjecting the filtered water to filtration by the RO unit or the nanofiltration membrane or membranes.