Rainwater harvesting can be a supplementary or primary water source for individual households or small communities, especially in locations with seasonal rainfall or limited surface water resources (e.g., small islands). The use of roof runoff or good quality stormwater for landscape irrigation or industrial uses (e.g., concrete production) in highly developed urban areas, or low flow maintenance in urban streams (see also Chapter 5) is attracting interest as a measure supporting environmental sustainability by reducing water supply demands and reducing urban runoff flows and their impacts.