Memcor(R) Continuous Microfiltration (CMF) is a technology that is very efficient for the clarification and disinfection of karstic waters for the production of drinking water. In Hericourt-en-Caux (Normandy), a Memcor(R) CMF plant is treating a particularly difficult water with a background level of turbidity between 3 and 30 NTU and recurrent events of several hundred NTU lasting between some hours and several days. The turbidity of the permeate is consistently between 0.1 and. 0.2 NTU. A fouling problem has been solved by injection of a coagulant and optimisation of the cleaning conditions.