A relatively new concept in the United States, the two-stage filtration process incorporates an initial bank of coarse filters, followed by a bank of final filters that are normally operated at a high filtration rate. Pilot studies showed that two-stage filtration is an attractive alternative to either conventional treatment or direct filtration, depending on the quality of the raw water. If the raw water frequently exhibits high turbidity or presents taste and odor problems, type 1 two-stage filtration, which includes flocculation and settling, should be considered as the treatment alternative. The type-2 two-stage process, involving neither flocculation nor settling, is suggested for cases in which the raw water quality if good enough to allow direct filtration. Pilot studies of each type of two-stage filtration are presented. Includes 3 references, tables, figures.