Rainwater

Rainwater harvesting is where rainwater is collected for garden purposes or, in more advanced systems, for lavatory cisterns and washing machines.  The simplest systems collect rainwater in a butt connected to a rainwater downpipe.  More sophisticated systems can include underground storage tanks, filters, pumps and water treatment plant.  

Rainwater harvesting is not a substitute for the mains water supply as untreated rainwater is not suitable for human consumption after it has been stored.  Any pipework should be marked clearly to distinguish it from mains water pipework, and the two systems must be kept separate at all times to prevent any contamination of the treated mains supply.  Rainwater is not chlorinated.  It is therefore more suitable for plant growth.  It can also save detergent in areas of hard water when used in a washing machine, but there can be issues with both colour and odour when poor-quality stored rainwater is used.

Where the mains supply is metered, the use of rainwater can reduce water bills, but the larger systems use pumps, and government research suggests that the operational carbon emissions associated with pumping the stored rainwater were generally higher than the carbon savings from the reduced mains water supply.  Rainwater harvesting is useful for reducing water bills and saving mains water, particularly in times of drought when the stored rainwater can be used. However, it is not a substitute for water efficiency where the use of mains water can be reduced through the use of low flow taps, aerated showers and low flush toilets.

A very useful guide on harvesting rainwater for domestic uses was published by the Environment Agency in 2010.  Legionella and other contamination issues are discussed in the guide from Page 15 onwards.  It is important to understand the potential health issues when considering a rainwater harvesting system.

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