An ozone-assisted physical-chemical treatment process involving the use of chemical coagulation-precipitation, clarification (either sedimentation or flotation) and filtration for cooling tower raw make-up water treatment, side-stream recirculating water treatment, or blowndown water treatment was investigated by the Lenox Institute of Water Technology (LIWT) using bench-scale laboratory tests, continuous pilot plant demonstration, and full-scale cooling tower operation. Only the preliminary laboratory data are introduced at this stage. The results show that 95 % of iron ions, 67.8 % of copper ions , 100 % of total coliform bacteria, and over 98 % of total hardness can be removed by the ozone-assisted dissolved air-ozone flotation and filtration (DAOFF) process system. The DAOFF system may be adopted for (a) production of cooling tower make-up water using raw reservoir/stream water or raw groundwater water as the source water; (b) treatment of cooling tower side-stream recirculation water for scale removal, new scale prevention, corrosion, bacteria disinfection, algae control and water purification; or (c) treatment of cooling tower blowdown water for final discharge to a deep well (without groundwater contamination), an ocean, or a receiving water (without thermal pollution nor excessive TDS). Ozone kills all bacteria slimes which commonly bind the scale on the metal surface, and keeps the hardness in suspension, so the suspended hardness will not form scale, and may be effectively removed by filtration.