The objective of conditioning water is to change the composition of water such that it is fit for the purpose for which it is intended. In many cases, the calcium – carbon dioxide balance of the water, or the aggressiveness (removable calcium) of the water has to be altered. This can be corrected by, for example, changing the acidity (by aeration or by dosing an acid or base) and the calcium content (by means of an ion exchanger or precipitation) of the water.