RainWater Harvesting Tank Size Calculator

In order to establish the required tank size for your rainwater harvesting system, please follow the below instructions that will guide you through the tank size calculator tool.

However If you need any further help please contact us on 020 8539 4707

1.  Please click the icon to download the Excel spreadsheet
2.  Insert your home's measurements, in metres, in the 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 on the "Rainfall" Tab and find out the average annual rainfall in centimetres in your part of the country. Then simply type this in the 3rd yellow box; e.g., if you live in East Anglia, the driest part of the country, use 63.
4.  Insert in the red box the number of days drought protection you would like from your rainwater harvesting system. You can change the number of weeks at will to see what impact it has on the tank size you need.
5.  The results of the calculations are shown in the three light blue boxes:
  5.1. The first blue box shows the amount of water you need to protect your home use and garden from drought.
  5.2. The 2nd blue box shows YES if your roof is big enough to provide the water you need to fill the tank!
  5.3. The 3rd blue box shows the tank size we would recommend.