This paper describes a large-scale nanofiltration (NF) plant at the Suburbs of Paris Utility that was started in 1999, and produces 140,000 m3/day of permeate. This water is blended with another 60,000 m3/day biologically produced water. Data was collected in 1998 and 1999 to document the distributed water quality before the change. Sampling campaigns were continued in 2000, 2001 and 2002 to determine the distributed water quality since NF started being used. Results show a lower formation of THMs, and a lower number of bacteria. Water quality continues to improve now, 3 years after the treatment change. Includes 8 references, tables.