Harvesting rainwater offers many advantages: It conserves municipal and well water; it is free; gravity fed systems conserve energy; it is low in salts and good for plants; and it can reduce flooding and erosion. Rainwater provides an excellent primary, supplementary, or alternative source of water. In terms of quality, it generally falls between groundwater and surface water. Rainwater can be used at multiple scales from residential to commercial and at the neighborhood or community level.