in the bulk of the water which has not been evaporated, thus raising the salt concentration in the circulating cooling water. To prevent the salt concentration of the water from becoming too high, a portion of the water is drawn off or blown down (D) for disposal. Fresh water make-up (M) is supplied to the tower basin to compensate for the loss of evaporated water, the windage loss water and the draw-off water. Using these flow rates and concentration dimensional units: A water balance around the entire system is then: Since the evaporated water (E) has no salts, a chloride balance around the system is: and, therefore: From a simplified heat balance around the cooling tower: Windage (or drift) losses (W) is the amount of total tower water flow that is entrained in the flow of air to the atmosphere. From large-scale industrial cooling towers, in the absence of manufacturer's data, it may be assumed to be: W = 0.3 to 1.0 percent of C for a natural draft cooling tower without windage drift eliminators W = 0.1 to 0.3 percent of C for an induced draft cooling tower without windage drift eliminators W = about 0.005 percent of C (or less) if the cooling tower has windage drift eliminators W = about 0.0005 percent of C (or less) if the cooling tower has windage drift eliminators and uses sea water as make-up water. Cycles of concentration Cycle of concentration represents the accumulation of dissolved minerals in the recirculating cooling water. Discharge of draw-off (or blowdown) is used principally to control the buildup of these minerals. The chemistry of the make-up water, including the amount of dissolved minerals, can vary widely. Make-up waters low in dissolved minerals such as those from surface water supplies (lakes, rivers etc.) tend to be aggressive to metals (corrosive). Make-up waters from ground water supplies (such as wells) are usually higher in minerals, and tend to be scaling (deposit minerals). Increasing the amount of minerals present in the water by cycling can make water less aggressive to piping; however, excessive levels of minerals can cause scaling problems. As the cycles of concentration increase, the water may not be able to hold the minerals in solution. When the solubility of these minerals have been exceeded they can precipitate out as mineral solids and cause fouling and heat exchange problems in the cooling tower or the heat