Safe drinking water should be free of pathogens, including parasites. For surface waters, obviously contaminated with Cryptosporidium oocysts, water treatment should include a filtration and a disinfection step. Two main processes are currently available for step disinfection: ozone treatment and UV irradiation. However, ozone treatment forms bromate ions, which are now regulated by European and American Disinfection byproduct (DBP) standards. Moreover, high costs of investment are necessary for the ozone contactor construction. UV irradiation, according to the current knowledge, does not form byproducts and due to a low level of fluence necessary to reach a high level of disinfection, Medium-Pressure UV (MP-UV) offers a cost-effective system and an interesting and pertinent alternative for the disinfection of surface water. This paper presents results obtained in a pilot study on sand filter effluent in the Neuilly-sur-Marne Water Treatment Plant (WTP), which currently delivers water to 1.5 million inhabitants in the suburbs of Paris, France. The focus of the research was on the question of where a UV step should be integrated in an existing water treatment line. Includes 12 references, table, figures.