During the last ten years much research has been conducted by KIWA, in close cooperation with various waterworks, into the rehabilitation of clogged production wells. During this research it became apparent that various types of clogging could be distinguished. One type of clogging is caused by the mixing of groundwaters with incompatible chemical compositions in the well itself, due to the vertical chemical heterogeneity of groundwater in the aquifer. Another type of clogging is caused by the increased velocity of groundwater flow near the borehole, which increases the intensity of various biological and chemical processes. The selection of the correct method of rehabilitation, the rehabilitation results, and the costs, all depend on the type of cloging that has occurred.