Rainwater

Rainwater is precipitation that falls to the earth and can be captured for use. When collected from rooftops or other catchment surfaces, it becomes a potential source of freshwater that is renewable in space and time. The quality of rainwater depends on the catchment area and exposure to pollutants, and it is generally not potable without treatment.

Harvesting systems typically include gutters, downspouts, screens, first-flush devices, storage tanks or cisterns, and distribution pipes. Filtration and disinfection, such as sediment filters, activated carbon, ultraviolet light, or chlorination, are used to improve safety for non-potable uses and, in some cases, for drinking after extensive treatment.

Common uses include landscape irrigation, toilet flushing, laundry, and other non-drinking household needs. In some regions with advanced treatment, rainwater can supplement drinking water supplies. On a larger scale, rainwater harvesting can reduce stormwater runoff, lessen demand on groundwater and municipal supplies, and contribute to flood management.

Regulations and safety: Backflow prevention and separation from the public potable water system are important to prevent cross-contamination. Maintenance is required to remove debris, inspect roofs and gutters, and prevent mosquito breeding in stored water.

Limitations include variable yields dependent on rainfall, catchment size, and storage capacity; quality can be affected by roofing materials, bird droppings, industrial pollutants, and air quality. Some rainwater requires treatment or must be avoided for drinking; costs depend on local climate, water prices, and required standards.