Rainwater harvesting represents an alternative water supply that captures and stores rainwater for later use. The harvesting of rainwater is as simple as collecting water from surfaces on which rain falls, and subsequently storing this water for later use. Normally, water is collected from building roofs and stored in dedicated water tanks.
Green roof technology is improving all the time. The goal is to keep the water clean, in some cases probably cleaner than from some traditional roof schemes. Naturally it is necessary to observe the stability characteristics of the sub-structure, the membranes, and the related maintenance requirements.