Tank Calculator Enter in box the nearest area, in square metres, of roof area drained Via, a single, or multiple, downpipe system. Measure the length and width of the plan area of the building and assess which downpipes collect this rainwater to the location of the storage tank. Tick box for area of country you live in for annual rainfall: Region Average annual rainfall SW England and S Wales 1316mm SE England and S Central England 846mm Midlands 938mm East Anglia 692mm NW England and N Wales 1368mm NE England and E England 833mm www.metoffice.gov.uk/climate/uk/2007/annual/averages1.html www.weatherstations.co.uk/aws_map.htm Roof profile Flat roof system Pitched roof system Tank sizing for drought protection 18 day protection or 5% 36 day protection or 10% Plant area watered visit RHS for guidance 1 litre per metre per day 1.7 litre per metre per day 2.4 litre per metre per day www.rhs.org.uk/advice/profiles0406/water.asp
