The tank size calculator is provided by RainWaterHarvesting.co.uk for the information of their customers and can be used to establish the size of tank you might decide to install. You will need to know the approximate dimensions of your house and of your garden.

1. Click on the link here and download the Excel spreadsheet if you are going to use rainwater in your garden, or Click on the link here and download the Excel spreadsheet if you are going to use rainwater in the house
2. Insert your home's measurements, in metres, in the first two yellow boxes. Try to estimate the dimensions of that part of the house from which you will be collecting rain water.
3. Refer to the table and find out the average annual rainfall in centimetres in your part of the country, then type it in the 3rd yellow box. E.g., if you live in East Anglia, the driest part of the country, use 63.
4. Insert your garden's measurements, in metres, in the 4th and 5th yellow boxes. Try to estimate the dimensions of that part of the garden you must protect against drought, i.e. exclude driveway, patio, scrubland and parts under trees.
5. Insert in the last yellow box the number of weeks drought protection you would like from your RainWaterHarvesting system. You can change the number of weeks at will to see what impact it has on the tank size you need.
6. The results of the calculations are shown in the four blue boxes:
6.1. The first blue box shows the amount of water you need to protect your garden from drought, using hand held hose to the base of plants or a trickle system.
6.2. The 2nd blue box shows the amount of water your roof can collect during the year (excluding the drought period of course).
6.3. The 3rd blue box shows YES if your roof is big enough to provide the water you need to fill the tank!
6.4. The 4th blue box shows the tank size we would recommend.

You're done! Congratulations. Go to the product page or search our site for tanks and the size you require, place an order and install the system. If you cannot work the spreadsheet calculator please email us the 6 figures to calculator@rainwaterharvesting.co.uk and we will email you the required tank size.


More details on rainfall round Britain on the Met Office web site at http://www.metoffice.gov.uk/climate/uk/2006/annual/averages1.html
More details about the amount of water required for plants at the Royal Horticultural Society web site at 
http://www.rhs.org.uk/advice/profiles0406/water.asp
If the calculator said that you need tank 7000 litres or bigger, don't be surprised. Most suburban homes in Britain will need this amount of water to protect against drought for just a week or two. If you want longer protection, then buy multiple tanks and connect them together (a few inches from the bottom) to increase your capacity.