Plants need the most water in hot, dry and windy weather, which is usually when water companies are least able to meet demand.
Less than 3 percent of the annual water consumption of an average household is estimated to be from garden use, but at peak demand as much as 70 percent of water supplied may be used in gardens. This surge in demand can lead to water companies being forced to deplete groundwater and streams, which can cause serious environmental damage as well as raising the cost of water for consumers. Gardeners should therefore use mains water as sparingly as they can.
Even in dry districts, 24,000 litres (5280 gallons or 150 water butts) could be collected from the roof each year. However, most water falls in winter, and would have to be stored for use in summer. There are about 18 weeks from May until September when plants' needs exceed rainfall. At first, the shortfall is met from soil reserves, but these can peter out by July, leading to about six weeks when watering is needed.
Even tiny gardens and patios can be used to collect and store rainwater, which may help the gardener get through hosepipe and sprinkler bans.