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The Collection, Conveyance and Storage of Rainwater for Later Use Commonly, rainwater harvesting systems are constructed of three primary segments; (1) a collection method, (2) a conveyance component and (3) a storage facility. Rainwater harvesting collection, conveyance and storage systems can be incorporated into almost any existing building, although it is easier to incorporate a rainwater harvesting system into new construction.  (1) A collection or catchment system is a simple structure comprised of roofs and/or gutters that direct the rainwater through a conveyance system and into a storage container. Roofs are ideal as catchment areas as they easily collect large volumes of rainwater. The amount and quality of rainwater collected from a catchment area depends upon the rain intensity, roof surface area and type of roofing material. For a 1,000 square foot roof, about 620 gallons of rainwater can be collected, per inch of rainfall, regardless of pitch.
(2) Conveyance components are required to
transfer the rainwater from the roof catchment to storage. Conveyance is usually accomplished by
connecting roof drains and piping from the catchment
area (or roof top) to one or more downspouts
that transport the rainwater through a filter system
to storage in tank or retention pond for reuse or
recharge.*A siphonic roof drainage system is one of the most effective technologies offered for capturing rainwater from a building roof top to aid in implementing rainwater harvesting. In a siphonic system several roof drain outlets can be connected to a single vertical discharge pipe. Fewer discharge points and no requirement for pitch in the piping means the rainwater can be easily routed horizontally below the roof to a storage tank or retention pond. One of the major benefits of designing a building with siphonic roof drainage and rainwater harvesting systems is reduced overall construction and facility operation costs. Additional benefits include reduced discharge of rainwater to lakes, streams, rivers and sanitary systems, and decreased dependence on municipal water supplies. 
(3) Storage tanks (or cisterns) for the harvested rainwater make
stored rainwater available when needed. Depending on the space available these
storage containers can be constructed above grade, partly underground, or below
grade. Various types of rainwater storage containers can be found in use. They
include cylindrical ferrocement tanks (reinforced
steel and concrete), mortar jars (large jar shaped
vessels constructed from wire reinforced mortar),
single and battery (interconnected) tanks made
of either galvanized steel, concrete, ferrocement,
fiberglass, or polyethylene, or they could be made
of wood, metal, or earth. Storage tanks should be
located as close to supply and demand points
as possible to reduce the distance the water is
conveyed.
The size of the storage container needed for a particular application is determined by the amount of water available for storage (a function of roof size and local rainfall), the amount of water likely to be used (a function of demand), and the projected length of time without rain, aesthetics, and budget. Before water is stored in a storage tank (or cistern), and prior to use, it should be filtered to remove particles and debris. Filtration is a key element in the storage and use of harvested rainwater. Upon leaving the tank, the stored water is extracted from the cleanest part of the tank, just below the surface of the water, using a floating filter. |
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