Water is trickled in open cooling towers. In the process it evaporates, leaving the salts it contains behind. The evaporation loss is compensated for by a constant supply of fresh water. Since the make-up water also carries salts, the concentration in the system increases continuously. This is called thickening. In Germany VDI 3803 defines upper concentration limits for this point. If these limits are exceeded (e.g. sulphate and chloride), either corrosion can be the result – or persistent, performance-reducing deposits are formed. The correct treatment of the make-up water, on the other hand, ensures durable, reliable and efficient operation.
The german VDI guideline 2047-2 defines rules for the hygienic operation of evaporative cooling systems. Water treatment also plays an important role in these guidelines.