A rainwater tank, also called a rain barrel in North America or a water butt in the UK, is any vessel used to collect and store rainwater that runs off roofs. Systems range from small aboveground barrels to large cisterns and underground tanks. Collected water can be held for months to supply gardens, laundries or nonpotable household needs during dry periods; see general information about the container concept for storage and handling.

Design and common components

Basic systems attach to gutters and downspouts and include a storage tank, an inlet, and an overflow. Typical features that improve performance are fine-mesh screens to keep debris and insects out, first-flush diverters that discard the initial runoff, outlets for gravity feed or pumps, and sealed lids to reduce contamination.

Materials and sizes

Tanks are made from plastic, metal, concrete or fiberglass. Small home barrels hold tens to a few hundred litres while household cisterns and commercial tanks can store thousands. Aboveground tanks are easier to install; buried tanks save space and temperature variability but require excavation and structural supports.

History and development

Collecting rainwater is an ancient practice: civilizations used cisterns and rock-cut reservoirs long before modern plumbing. Interest in domestic rainwater harvesting has grown with concerns about water conservation, stormwater runoff, and resilience to drought, prompting improved filters, standards and integrated systems.

Uses, benefits and examples

  • Garden and landscape irrigation, reducing demand on municipal supplies.
  • Toilet flushing, laundry and other nonpotable indoor uses when properly plumbed and treated.
  • Fire protection, livestock watering and irrigation on farms or remote properties.
  • Stormwater management—storing runoff reduces peak flows and erosion in urban areas.

Maintenance, safety and regulation

Regular maintenance includes cleaning gutters and filters, checking seals and pumps, and ensuring screens prevent mosquito breeding. Rainwater is not automatically safe to drink; potable use requires filtration and disinfection or certification. Collection is regulated in some places: local codes can limit use, require backflow prevention, or, in rare cases, restrict harvesting altogether—consult local authorities if collection is forbidden in some jurisdictions. Seasonal planning can maximize benefit by storing wet-season supply for drier months.

Notable distinctions: a "rain barrel" typically denotes a small, simple aboveground unit, while "cistern" usually refers to larger-capacity or buried systems integrated into plumbing. Proper design balances storage size, roof area, climate and intended uses.