www.RainWaterHarvesting.co.uk Client and details

TANK SIZE CALCULATOR ©2009 RainWaterHarvesting.co.uk

Insert your building's data in the yellow boxes. Change the red box to suit your needs.

From the roof area off your property, you assess the amount of water available, and equate it to the amount you will use.

1 Main Building area

Building width (metres) 14

Building depth(metres) 10

Rain Collection Area 1 140

2 First extension/conservatory/porch/garage/shed etc

width (metres)

Depth (metres)

Rain Collection Area 2 0

3 Second extension/conservatory/porch/garage/shed etc

width (metres)

Depth (metres)

Rain Collection Area 3 0

4 Third extension/conservatory/porch/garage/shed etc

width (metres)

Depth (metres)

Rain Collection Area 4 0

5 Calculate the area of any remaining useful roofs as a figure

in square metres and enter directly in the yellow box to the right 0

6 TOTAL of collectable roof areas (square metres) 140

7 Maximum rainwater which could be collected

Rainfall per year in your area (cms). Use rainfall chart on sheet 2, a figure between 60 and 170. 113

8 Collectable rainwater per annum (in litres - discounted by 20% to account for water loss) 126,560

9 Use of water in the building

Washing machine and toilet flushing are the main usage for rain water in domestic systems. Add an allowance for daily garden use.

Number of people in the house 3 litres

Number of clothes washing cycles per day (50 litres each) 0.8 38

Number of toilet flushes per day (average 5 litres each) 13 66

Outdoor use per day (min 5 litres per person per day) or adjust till F46 = F35 more or less 15

10 Amount of water you require every day or in a year

every day 119

Rainwater DEMAND per annum 43,362

11 How many days drought protection do you need?

In the Summer of 2006 in SE England there was almost no rain for 77 days

between June 1 and August 18. Enter a number of days in the red box. Optimal is 18 to 21 days. 21

12 Capacity of water storage in litres required for drought protection 2,495

The lesser of YIELD or DEMAND per annum 43,362

Therefore, volume of rainwater storage required 2,495

Sufficient roof water available (CONCLUSION): YES

Tank size required from RainWaterHarvesting (CONCLUSION): USE 2700 LITRE Carat TANK

5% of annual rainwater yield (in litres) 6,328

5% of annual non-potable water demand in the home (in litres) 2,168

Tank must hold at least … (in litres) 2,168

Tank size required from RainWaterHarvesting (BSI requirement): USE 2700 LITRE Carat TANK

Check stock and prices at www.rainwaterharvesting .co.uk or by email at info@rainwaterharvesting.co.uk

Oct08 MB. Rev 5 Jun09 MB (BSI check added). Rev 6 Nov09 Text tab changed

Based on British Standard BS8515, 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.

2006 Actual % 0f average Average 1961-1990

Annual rainfall in centimetres cms

UK 118 107 110England 85 103 83Wales 142 101 141Scotland 165 112 147N Ireland 116 105 110England & Wales 93 103 90England N 102 108 94England S 76 99 77Scotland N 182 113 161Scotland E 117 106 111Scotland W 194 116 168England E & NE 79 105 75England NW & Wales N 140 110 128Midlands 80 104 77East Anglia 63 105 60England SW & Wales S 113 93 121England SE & central S 79 104 76

1) We attach the Tank Size calculator completed with your figures showing

a roof area of… 140 square metres,

annual rainfall in your area of … 113 centimetresand, therefore, total annual collectable rain (discounted by 20% to account for

water loss washing the leaves out) of… 126,560 litres

2) We have then calculated your typical daily usage of rain water indoors

and in the garden

A washing machine cycle needs 50 litres and we assume… 1 cycles per day

Toilets require 4.42 litres per (low) flush, and we assume... 13 flushes per day

We assume some water needed in the garden etc. of… 15 litres per day

This makes a total daily use of … 119 litres per day

which is the same as … 43,362 litres per year

Are you able to collect sufficient water from the roof to supply your annual

needs? YES

3) We have assumed you would require drought protection of … 21 days.

The optimal quantity of stored water, from first principles, is … 2,495 litres

The tank size calculator is now telling you that you need to… USE 2700 LITRE Carat TANK

4) Based on British Standard BS8515, 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. These figures

check the tank size requirement above.

5% of annual rainwater yield … 6,328 litres

5% of annual non-potable water demand in the home … 2,168 litres

To conform with BS 8515-2009, tank must hold at least ... 2,168 litres

Tank size required from RainWaterHarvesting (BS 8515-2009)… USE 2700 LITRE Carat TANK