Rainwater Harvesting Key Climate Change Role in Sustainable Water Supply
England will not have enough water to meet demand by 2040, according to the Environment Agency. But with rainwater harvesting playing a key role in a sustainable supply of water to the home and garden, average daily use could be cut from 140 litres to 100 litres.
Extreme heatwaves are increasing in frequency, which has seen summer temperatures reaching a record-breaking 38.7C (101.7F) in July 2019, beating the previous UK record of 38.5C (101.3F) in 2003. It’s predicted that there could be 50-80 per cent less water in a number of UK rivers during the summer months.
The impact of climate change to produce drastic temperatures is not the only trigger that has often led to significantly reduced groundwater reserves. The UK population is expected to rise from 67 million to 75 million by 2050, with an accompanying steep rise the demand for water. The need to address the challenges of an increasingly scarce natural resource has seen rainwater harvesting more readily accepted as a natural, sustainable way to reduce reliance on the mains supply as the sole source of potable water.
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Rainwater harvesting system depends on tank size, roof area and water usage
Rainwater harvesting systems operate by simply gathering roof water with the use of guttering and downpipes, then filtering-out solid matter before storing underground for later use. The stored water is then delivered through separate pipework to applications which do not require potable water, such as toilets, washing machines and garden taps.
A rainwater harvesting system is calculated to collect around 0.62 gallons of water per square foot of roof area, per inch of rainfall. Just a half inch of rain falling on a 1,000-square-foot roof will, therefore, be likely to yield 300 gallons of water. Of course, during heavy rainfall periods, the yield will be considerably higher. Storage tanks provide around 20-days consumption in dry weather from full capacity.
Suitability for an individual property will vary, depending on tank size, roof area and water usage. Some domestic roofs may be too small to provide the required capacity. Plus, drainage can vary from 0.9 on a steep pitched roof to 0.4 on a flat gravel roof. However, it is estimated that, on average, half of British households’ water usage can be supplied from rainwater.
A simple formula for the amount collected per year by a rainwater harvesting system is typically calculated as:
Roof area (m2) X Drainage area X Filter efficiency X Annual rainfall (mm) = Total litres collected per annuum.
Installing a rainwater harvesting system – clear practical and economic reasons
Notwithstanding, the all-important climate change issue, the clear practical and economic reasons for installing a rainwater harvesting system in the average home have accelerated in recent years. Saving money may often be a key factor – by up 50 per cent of mains water costs in some areas – but there are other strategic benefits. For example, use of natural soft rainwater in hardwater regions, plus control over the source of water, how it is treated and used.
Investment in a rainwater harvesting system in increasingly seen as an immediate response to climate change and the impact on producing extreme weather events, such as escalating heatwaves as well as the long term benefit on alleviating overall water supply.
Rainwater harvesting included in Government Code for Sustainable Homes
It was back in December 2006 that the Government introduced its Code for Sustainable Homes including, the specifications for rainwater recycling and, “the appropriate collection and storage of rain from hard outdoor surfaces for use instead of potable water in WCs and/or washing machines”.
Key criteria are:
- No open access at the top of the collector (a child-proof lid is allowed).
- Provision of a tap or other arrangement for drawing off water.
- Connection to the rainwater downpipes with an automatic overflow into the conventional rainwater drainage system.
- A means of detaching the rainwater downpipe and access provision to enable the interior to be cleaned.
- A collection system sited outside and not buried must be stable and adequately supported. The material used for the container shall be durable and opaque to sunlight.
- A system that is part of a rainwater collection system providing internal water use requires water for external use to be provided in a separate tank. This could be an overflow pipe leading from the main tank to a correctly specified water butt for external water use.