Rainwater tank size is calculated from three factors: the roof catchment area, the local annual rainfall, and the garden's irrigation demand. A roof of 100 square metres in Surrey, which receives around 600 to 700mm of rain a year, can collect around 60,000 to 70,000 litres a year. The tank is sized to store enough to bridge dry spells, not to hold a full year's rainfall. A typical private garden system uses a 5,000 to 10,000 litre underground tank; an estate might use 10,000 to 30,000 litres or more. A mains top-up kit keeps the tank topped up when rainwater runs low, so the system never runs dry. We calculate the correct tank size during the survey so it is matched to your roof, rainfall and garden.
Frequently Asked Questions
What size rainwater tank do I need for irrigation?
A typical private garden uses a 5,000 to 10,000 litre tank; an estate might use 10,000 to 30,000 litres. We calculate the correct size from your roof, rainfall and garden demand.
What happens if the rainwater tank runs dry?
A mains top-up kit keeps the tank topped up automatically when rainwater runs low, so irrigation continues uninterrupted.