At the moment steam condenses, condensate water is formed. A condensate system is a two-phase system, in which there is at the same time a gas (steam) and a liquid (condensate) in the pipes. Both are separated by steam traps.
The use of condensate can be very useful from an energetic point of view because it can often return to the steam boiler at a high temperature. Moreover, it is already of a particularly good quality and contains little or no salts.
But during transport to the steam boiler house, impurities can enter the condensate water from the pipe network. As a result, the condensate must be 'polished' in some cases before being used again. This usually happens with ion exchange.