The following list will summarize is a collection of links to some of the better water reuse sites on the web:
CSIRO Land and Water - Loads of publications available for free from Australia.
AWWA - American Water Works Association, one of the bigger American organizations.
U.S. Bureau of Reclamation - Another large American government organization.
Watereuse.org - A website that highlights information mainly from California.
Singapore NEWater - Detailed information on Singapore's water reuse project
Water Recycling 2030: Recommendations of California’s Recycled Water Task Force
United States EPA
Sanitation Connection - An excellent list of links to all sorts of different water reuse sites.