Water: collecting, storing and re-using

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.

Rainwater can be collected from the roofs of homes, garages, greenhouses and other garden structures as long as they have gutters and a drain pipe.

Water butts are designed to collect water from either open or closed drain pipes. Closed drain pipes can be easily tapped into with a rain water diverter kit.

Clean water butts annually to prevent disease spread. use collected water on established plants rather than seedlings. If multiple butts are used, rotate use to keep stores fresh.

Local councils and DIY stores are good places to purchase basic plastic water butts. It is easier to access the water if the butt has a tap at the base and sits on a stand, either ready-made or improvised with a pile of bricks. More expensive butts moulded to look like beehives or terracotta urns are an attractive option, as are recycled wooden barrels.

As climatic change models suggest an increasing proportion of rain will fall in winter, it may become cost effective to build-in rainwater storage when constructing new homes. This usually involves sinking a large tank somewhere in the garden, pumping water out for use in the garden or for domestic tasks such as flushing toilets. However, the more pumps and piping that is required, the greater the cost and carbon footprint of such schemes.

The UK Rainwater Management Association can advise on purchase and installation of rainwater harvesting systems.

Domestic wastewater (known as ‘grey water’) may also be used in the garden. This may be from the kitchen, the washing machine or baths, basins and showers. 'Black water' from WCs should always be consigned to the sewerage system and never used in the garden. Water from septic tanks is best not used either.

Household soaps and detergents are harmless to plants, but water containing bleaches, disinfectants, dishwasher salt and stronger cleaning products should not be used, as they can harm plants and even damage soil structure if used long-term on soil.

It is prudent to alternate containers used for wastewater and mains or rainwater, to prevent build up of potentially harmful residues and bacteria. It is also sensible to avoid using grey water on salads and other produce to be used without cooking.

Grey water should be used as it is produced and storage avoided. If left potentially harmful organisms might multiply and it will certainly smell most unsavoury.

Drought-resistant gardening
Gardening in a changing climate website
Sustainable gardening
UK Rainwater Management Association
Watering
Water: using softened and other types
Water-retaining granules