Rainwater Harvesting
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4 |
Reduces potable water consumption required for irrigation and indoor fixtures, where rainwater is plentiful and regularly occurring |
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3 |
One to five years for large-scale systems |
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3 |
Engineering services for large-scale systems and cisterns or tanks, and treatment systems for large scale systems |
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FAC, FIN, BPO |
Rainwater may be captured and collected in underground, surface, or elevated tanks for immediate irrigation use or treated for potable uses. In locations with extreme water shortages, rainwater may be treated to a potable level and used to supply building systems.
The feasibility of large-scale rainwater harvesting in a particular location is highly dependent upon the amount, intensity, and yearly distribution of rainfall, as well as the cost and availability of purchased water. As rainfall is rarely distributed evenly throughout the year, rainwater is most often used as a supplementary water source. When rainfall is distributed evenly throughout the year, storage tanks can be smaller, thus reducing the capital cost.
Capturing and reusing nine million L (2.4 million gal) of rainwater every year is equivalent of 50,000 bathtubs full of water.
Rainwater collection systems require filters or first-flush diversion treatment to eliminate solids often found in the initial runoff from a rainfall event. Because water from roof surfaces usually contains fewer impurities (oils, heavy metals, and fertilizers) than surface-level water, roofs are typically the first source for rainwater harvesting. Stormwater collection from site surface runoff can be collected in an underground cistern or pond and reused for irrigation or treated appropriately for reuse for non-potable uses, such as sewage conveyance.
Rainwater system maintenance is generally limited to annual cleaning of the storage tank and regular inspection of filters, gutters, and downspouts. Maintenance typically consists of the removal of dirt, leaves, and other accumulated materials. Such cleaning should take place before the start of the major rainfall season or forecasted storm event.
Elevated storage has the advantage of gravity feed. Surface-level tanks require additional care to avoid damage and contamination by people and animals, and may require fencing.