A method and composition are provided for the operation of an evaporative cooling tower with minimal, or no, blowdown. In some embodiments, the method involves using sodium cation-exchanged softened water as makeup water for the cooling tower, providing a bypass filter for suspended solids removal from the cooling water, treating the cooling water with a composition for control of corrosion and deposition, and using an effective biocide for control of biological growth within the cooling tower system. In some embodiments, a composition is provided that comprises AMPS acrylic terpolymer, sodium silicate, phosphate ions, and polyphosphate ions. When dosed at the recommended levels, the composition controls corrosion of cooling system materials to generally acceptable levels in spite of the extremely corrosive environment resulting from the cycling of sodium cation-exchanged softened water in the cooling tower.