Two new cooling towers were started up on ZLD water chemistry at a major steel mill to minimize discharge waste treatment costs and reduce water use. High TDS (total dissolved solids) water chemistry that results from ZLD required new scale and corrosion inhibition technology to protect galvanized and steel surfaces. After two years operation, galvanized tubes and mild steel in systems show outstanding corrosion protection, control of “white rust” and no scale at TDS up to 150,000 in tower water. New technology that produces inhibitor chemistry from source water silica permits operation at high TDS without scale or corrosion, and provides biostatic water chemistry. Water treatment costs are less than traditional chemical treatment, and chemical handling and storage is eliminated.