Makeup water is fresh water added to the cooling tower basin to replace water lost through evaporation, drift, and blowdown. In a typical cooling tower, evaporation accounts for 1-2% of circulating flow, drift losses range from 0.1-0.3%, and blowdown removes another 0.5-2% depending on water quality and cycles of concentration. Maintaining adequate makeup water supply is essential for continuous tower operation.
Water Supply Requirements
Makeup water volume depends on tower design, operating conditions, and water treatment practices. A 500-ton tower circulating 1,200 gallons per minute may require 20-30 gallons per minute of makeup water under typical operating conditions. Water source options include city supply, groundwater wells, recycled wastewater, or rainwater collection systems. Water quality significantly affects makeup requirements, as poor quality water requires higher blowdown rates and increases chemical treatment costs.
Operational Management
Automatic float valves regulate makeup water level in the basin, maintaining 3-6 inches above the sump pump intake. Water hardness, pH, alkalinity, and dissolved solids require testing and chemical adjustment to prevent scaling and corrosion. Dual makeup sources improve system reliability during supply interruptions. In water-scarce regions, cooling tower design emphasizes low makeup water consumption through higher cycles of concentration and waterless heat rejection alternatives.