Over 97 percent of the 1.4 billion cubic kilometres of water on earth is sea water – unusable water. The majority of the remaining freshwater is permanently frozen in glaciers and the Poles.

Only 0.3% of the World’s total water resource is freely usable freshwater.

Then there is the bigger problem of the reducing quality of mains water. Purification is becoming increasingly difficult and expensive because of the increased pollution caused by nitrates, pesticides, phosphates and other chemical substances. This means that the freshwater reserve is being used in a permanent cycle.

The Environment Agency says that the average consumption of freshwater in the UK is 150 litres, per person, per day.

The answer to this is to replace mains water with untreated rainwater. For some domestic applications, the quality of purified water is unimportant. A typical household can save almost 50% mains water and in a commercial or agricultural environment, this saving can rise to 90% as rainwater can be used for livestock.