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[[File:Cistern Size.png|thumb|Schematic diagram of the inputs and outputs to a rainwater harvesting cistern]]
 
[[File:Cistern Size.png|thumb|Schematic diagram of the inputs and outputs to a rainwater harvesting cistern]]
 
===Simple===
 
===Simple===
{{plainlist|
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*Five percent of the average annual yield can be estimated:
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*<strong>Y<sub>0.05</sub>= A × C<sub>vol, A</sub> × R<sub>a</sub> × e × 0.05</strong>
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*Y<sub>0.05</sub> = Five percent of the average annual yield (L)
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*A = The catchment area (m<sup>2</sup>)
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*C<sub>vol, A</sub> = The annual runoff coefficient for the catchment
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*R<sub>a</sub> = The average annual rainfall depth (mm)
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*e = The efficiency of the pre-storage filter}}
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Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information.
 
Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information.
 
In a study of three sites in Ontario, STEP found the annual C<sub>vol, A</sub> of the rooftops to be around 0.8 [http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/performance-evaluation-of-rainwater-harvesting-systems-toronto-ontario/]. This figure includes losses to evaporation, snow being blown off the roof, and number of overflow events.<br>
 
In a study of three sites in Ontario, STEP found the annual C<sub>vol, A</sub> of the rooftops to be around 0.8 [http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/performance-evaluation-of-rainwater-harvesting-systems-toronto-ontario/]. This figure includes losses to evaporation, snow being blown off the roof, and number of overflow events.<br>
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