Which type of water should be considered an alternative water source?

Rainwater is considered an alternative water source because it is a sustainable source of water that is not supplied from fresh surface water or groundwater. Rainwater can be harvested from roofs or other surfaces and stored for later use. Rainwater can offset the demand for freshwater and reduce the pressure on water resources. Rainwater can be used for various purposes, such as irrigation, toilet flushing, cooling, and cleaning. LEED projects can earn credits for using alternative water sources under the Water Efficiency category. References: Best Management Practice #14: Alternative Water Sources1; LEED v4 BD+C Reference Guide, Water Efficiency, page 51