The groundwater is fed by infiltrating rainwater, which collects after penetrating several soil layers on a water-retaining layer. The oxygen contained in the rainwater converts to carbon dioxide due to chemical processes. This in turn reacts with the already "collected" groundwater. This process gives rise to carbon dioxide, which dissolves two soil elements.
Water-soluble iron and manganese are formed as part of this reaction chain. With renewed supply of oxygen by precipitation, these two elements oxidize and flocculate. The same effect occurs when through very intensive use of a well oxygen is "flushed in" by fast flowing and much flowing water.
The mostly brown colored flocculations settle on the filter edges, slits and in the advanced stage also on the filter stones. These incrustations are referred to as the sintering or oozing of the well. An increased presence of iron in the ground or a well reinforcement accelerates the clogging.