Rainwater Harvesting Calculator
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Insert your building's data in the yellow boxes.
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From the roof area off your property, you assess the amount of water available, and equate it to the amount you will use.
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Main Building area
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Roof width (metres)
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Roof length (metres)
1
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Roof Angle45
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Rain Collection Area (square metres)
1.90
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Calculate the area of any remaining useful
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roofs as a figure in square metres and
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enter directly in the yellow box to the right
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TOTAL of rain collectable area (sq metres)
1.90
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England SW & Wales S
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Average rainfall on a square metre according to Met Office (in cms)
105.00
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Annual rainwater yield in your area (in litres)
19,987.74
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How many people live in the household?
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Average yearly household water use according
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to Consumer Council of Water (in litres)
233,180.00
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Based on British Standard BS 8515, the rainwater
tank must be big enough to hold 5% of the annual
rainwater yield, or 5% of the annual non-potable water
demand, whichever is the lesser. The figures below
serve as a check against the tank size recommended above.
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5% of annual rainwater yield (in litres)
999.39
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5% of annual non-potable water demand in the home (in litres)
11,659.00
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To be conform to BS8515, tank must hold at least … (in litres)
999.39
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