Cooling towers concentrate dissolved and suspended constituents through evaporation (cycles of concentration), which creates three characteristic water-quality problems:
Scaling — as evaporation concentrates dissolved minerals (particularly calcium carbonate and calcium sulfate), the Langelier Saturation Index rises and scale precipitates on heat-exchange surfaces, reducing heat transfer efficiency.
Corrosion — dissolved oxygen, low pH, and elevated chloride concentration (also concentrated by evaporation) attack the metal components of the cooling system, particularly carbon-steel piping and heat exchangers.
Biological fouling and microbial growth — the warm, aerated, nutrient-rich environment of a cooling tower promotes algae, biofilm and slime growth, and specifically Legionella bacteria, which is a recognized public-health hazard from cooling tower aerosol drift.
