The term encompasses a variety of systems and facilities for collecting and storing rainwater for use in homes or businesses. Perhaps the simplest form is the traditional rain barrel that collects water off the roof. The collected water sometimes can be used for drinking but that depends on the condition and construction of the roof, and drains, and how much dirt or foreign substances collect off the roof along with the water, e.g. dust, mosses, twigs, bird droppings, pesticides and other pollutants, especially in urban areas. If dirty or contaminated, there are filters that might solve the problem. Otherwise the collected rainwater can be used to flush toilets, take baths, wash clothes and dishes and cars, and water gardens.
Even if you rely on private wells or other non-public water sources or do not pay for your water, harvesting rainwater can be very valuable in times of drought. During this past summer of 2010 many parts of the island of Ireland experienced a drought and water shortages. With climate change, such droughts may well increase in frequency and duration. In Donegal we were able to survive for three weeks without a water source (natural spring) by using the water from two rain barrels, one collecting the water from a barn and one from the house, for toilet, baths, and washing dishes. While there were short light showers during the three weeks that did not replenish the groundwater, the showers provided enough rain to re-fill the rain barrels.
More elaborate systems typically include a series of pipes and large containers, often of concrete or plastic, and pumps. The storage containers can be constructed on the roof or on the ground, or more typically underground.
In urban areas, collecting rainwater off roofs also has the benefit of reducing runoff water from entering stormwater systems and, if there is a combined sewer system, from overloading the system and discharging sewage back into homes or into surface water bodies during storm events.
Some further ideas to explore on Rainwater Harvesting:
Research the typical or average amount of rainfall for your area/school/community and find resources to help you calculate how much rainfall can be collected and stored.
Calculate how much water your school, family, group, or community uses for non-drinking purposes.
Then determine how you can collect the rainfall and what storage facilities you need to collect the water.
Estimate how much a rainwater harvesting system would cost to install and compare that cost to water service charges for public water supplies that are used for non-drinking purposes.
European Environment Agency, “Ecovillage,” on the ecovillage at Cloughjordan, County Tipperary, including its rainwater harvesting system (September 2010).
Tony Cain, “Harvesting rain for more sustainable water use,” The Engineers Journal (Vol. 64: Issue 5, June 2010). www.engineersjournal.ie/issues/june-2010/articles/rainwaterharvesting/
Calling Time on Waste: A publican’s handbook to a leaner, greener cost base (May 2009) (including use of rainwater harvesting).
HarvestH2O: the online rainwater harvesting community www.harvesth2o.com/
US Environmental Protection Agency, Managing Wet Weather with Green Infrastructure: Municipal Handbook, with a chapter on Rainwater Harvesting Policies cfpub.epa.gov/npdes/greeninfrastructure/munichandbook.cfm