Oxidation of dissolved Organic materials with Ozone results in polar and charged molecules that can react with Polyvalent Aluminum or Calcium to form precipitates. Treatment of surface water with up to 0.5 ppm of Ozone results in a decrease in turbidity, improved settleability, and a reduction in the number of particles. This treatment, referred to as pre-ozonation, destabilizes the colloid with a resulting reduction in the amount of coagulant needed to produce a clear filtrate.