Rainwater Harvesting FAQs
What is Rainwater Harvesting?
Rainwater harvesting is a way of saving the rainwater which would normally flow off a roof and down the drain, and using it as piped water to flush toilets and for the garden watering, yard washdown, vehicle and car washing, and even for your washing machine, instead of using expensive treated drinking (potable) water.
How does rainwater harvesting work?
A storage tank is fitted to your stormwater drain from your roof, and falling rain enters the tank through a filter which removes leaves and other matter. The storage tank is usually buried under car or vehicle parks, a garden or under the entrance access or drive, and contains a pump which pumps the rainwater to the building where it is piped to the toilets, and to the outside taps. Above ground tanks are also available.
Is rainwater harvesting suitable for work as well as at home?
Yes, in schools, hospitals, offices, commercial premises, rainwater can typically be used for toilets, vehicle washing, yard washdown and watering plant pots/gardens.
How much water can a system save?
Depending on your normal usage, it can save 30 to 50% of the treated drinking water from the mains in houses and up to and up to 80% of the treated drinking water in a business or commercial building.
How much would this save on water bills?
Depending on your normal usage, it can save 30 to 50% for the domestic user and 80% for the commercial user of the treated drinking water from the mains. Having metered water is the best way of appreciating the difference.
How much rainwater does a system collect?
This depends on the area and angle of your roof, and your rainfall. Averages of 100,000 litres per household are commonly quoted, much more for large roofed commercial buildings.
What can you use the water for?
Filtered, untreated rainwater should only be used for non- drinking or bathing purposes: toilet flushing, gardens and vehicle or yard washdowns.
Is it only for new buildings?
No, rainwater harvesting can be installed in existing buildings and integrated into your existing plumbing system.
Is it only for houses?
No, bungalows and commercial premises are also very suitable, the only limitation is the area of the roof to capture rain, in fact commercial and industrial buildings can make the largest savings.
Where is it installed?
The tank should be buried under a car or vehicle park, landscaped area, garden, patio or drive, with space left for the round access cover. Most systems are designed so that they can accept cars driving over them if suitably installed. Or an above ground system can be installed next to the house or property.
How much does it cost?
Domestic systems can cost from about £2500 up to £4000 plus including installation costs, depending on size of tank. Commercial systems can cost a lot more depending on size and requirement, but usually have a much quicker 'pay back' period due to the size of roof and high usage.
Are there any grants available?
Not for domestic installations yet, although several organisations are petitioning the government for assistance. For commercial installations, there is a tax relief scheme (ECA) for suitable approved equipment on the Water Technology List.
So, why should people buy Rainwater Harvesting systems?
To save on water bills and show they use water, an increasingly precious resource, responsibly to make a difference to our environment.
How clean is the water?
The rainwater is filtered as it enters the storage tank, to remove particles and other matter. It is kept in the dark and kept oxygenated to discourage algal growth, and properly designed systems are designed with calming inlets, which ensure that any sediment at the bottom of the tank does not get stirred up. The water is not drinking water fit for humans.
Could rainwater get into my drinking supply?
Not in a properly designed system, the pipework is entirely separate and should be identified as non-potable.
Do I need a big roof area to make it worthwhile?
No, most domestic roofs are more than adequate, but the bigger and flatter the roof area, the more rain will be captured, and the more the rainwater will substitute for treated mains water.
What happens when there is no rain?
When there is a prolonged spell without rain, the water level in the storage tank will fall to a minimum level. At this level, a float switch will open a valve from the normal mains supply and keep the storage tank topped up, until it is filled by rain again. Normal system design should allow up to a week without rain, given normal usage.
Can it be used when there is a hosepipe ban?
It is possible to use a hosepipe connected to a rainwater tank, provided that the tank is not connected to a mains water supply. Many people are doing this already by using a water butt.
Do I need to have a water meter?
Not absolutely necessary although, without a water meter your water provider will make the same blanket charge for all your unmetered water usage. Commercial premises will be metered, and the beneficial effects of rainwater harvesting should be seen very quickly.
How is the system maintained?
The internal filter should be washed about once a quarter, otherwise maintenance is not needed. The only moving components - pump and float switch have an extremely long life. The system should be designed to overflow a few times a year, to remove floating matter.
Is Rainwater Harvesting a new idea?
No, collection re-use of rainwater from roofs can be traced back thousands of years in hot, dry countries around the Mediterranean. In continental Europe, some 100,000 are installed annually; Germany has been using and refining the technology since the early 80s.
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