Domestic rainwater collection offers certain economic and environmental benefits: The water collected is free to use and saves on energy that might otherwise be used to treat and pump water from a municipal source. Installation of a rainwater collection system requires some initial expense, the extent of which depends in part on how you plan to use the water.
Collection
Rooftops are the primary source of rainwater collection, as the process involved is fairly straightforward and inexpensive. As the rainwater lands on the top of a building, it drips into gutters that are affixed to the edges of the roof. The water is then funneled through a downspout and into a large barrel fitted with a screen on top in order to prevent debris from entering. As an added benefit, the screen also prevents mosquitoes from breeding in the water.
Storage
The barrels used to hold rainwater are also known as cisterns and generally hold between 200 and 1,000 gallons of water. Some collection systems use a single barrel, while others use two or more barrels joined together by hose and connected to a single spigot. The ideal location for a cistern is on solid, level ground with enough distance from the home to accommodate the discharge of overflow water. The city of Seattle, for example, suggests that for homes with a basement, a distance of 10 feet is appropriate, otherwise 5 feet may be sufficient. Local governments often have their own specific permitting requirements.
Uses
There are a number of ways to use rainwater, with gardening being one of the more common. In some areas, collected water is used directly in irrigation. Additionally, homeowners can design gardens to take advantage of runoff by situating them in a depressed area with a soil that drains well. Alternative uses of rainwater include car washing, laundry and showering. Some regions may have more stringent limitations than others regarding how homeowners can use rainwater, which can affect the implementation and use of a rainwater collection system.
Treatment
Rainwater is naturally low in mineral content, which means that no additional "softening" is generally required. In many cases, collected water is used as is; however, indoor use demands special treatment in order to eliminate risks posed by contaminants. For toilet flushing and laundering purposes, simple pressure filters may be sufficient. In areas where use of rainwater for cooking or drinking is permitted, additional treatment is often necessary, as drinking untreated rainwater brings the risk of contracting diseases such as listeria and leptospirosis. The University of Hawaii at Manoa's College of Tropical Agriculture and Human Resources suggests the use of a UV sterilizer to eliminate risks posed by microorganisms.
Considerations
The type of roofing material used can affect the quality of the rainwater collected. For example, wood shingles are sometimes treated with herbicides in order to prevent rot and mold, which may render collected water unsuitable for gardening. Similarly, roofs containing copper or zinc materials may also leach contaminants into the water. Rooftops made of enameled steel and glazed tile generally produce few contaminants and are well suited for plant irrigation.
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