Available sources include but are not limited to the following:

Air-conditioning condensate is a good source. Cold condensate is generally cleaner than other potential sources and provides an efficiency advantage compared with other sources.
Harvested rainwater or stormwater can be used, especially if the project building has large surfaces that facilitate collection.
Graywater may be used if it is treated to an appropriate quality. Consult state or local ordinances to determine whether this is a viable option for your building.
Desalinated ocean water may be used if appropriately treated, but the desalinization process is fairly energy-intensive.
In some areas, municipal utilities offer a non-potable, reclaimed water supply, or so-called purple-pipe system (often plumbed in purple pipes to clearly differentiate it from potable water).
Naturally occurring surface and groundwater do not qualify as appropriate non-potable sources for LEED purposes.