Well bore clogging is caused by accumulation of particles on the well bore. However, all abstracted groundwaters contain particles, but not all wells clog. Apparently, clogging is not caused by the mere presence of particles, but other factors are also involved. Results from on-line well-head readings demonstrate that the clogging rate is not constant: the specific capacity decreases during long abstraction periods and remains constant during intermittent abstraction. Results of particle counts reveal that the particle concentration in the abstracted groundwater shows a peak immediately after switching on the well. This concentration peak is caused by the removal of particles from the well bore that accumulated during the preceding abstraction period. As long as all accumulated particles are removed, no clogging will occur; if not, clogging will occur. Consequently, well bore clogging can be prevented by switching the pump on and off with sufficient frequency to remove the particles accumulated on the well bore during the preceding abstraction period. Moreover, this explanation leads to additional recommendations for well operation, well construction and well design to prevent well bore clogging. © 2009 Springer-Verlag.