The simplest form of rainwater harvesting in the UK is the good old water butt standing under a downpipe and used to water the garden in summer. Nowadays they are usually manufactured from green heavy duty polyethylene or polypropylene and fitted with a tap to drain off water as required.
Rainwater harvesting has progressed from that scenario to encompass more significant yields from large buildings using new technology to deliver maintenance free systems. Most garden water butts hold between 100 and 300 litres; however these can fill very quickly during a significant rainfall event. If a downpipe is collecting water from a reasonably large roof area (e.g. all of the front or rear of a house) a much larger storage volume can be justified. So a roof of only say 30m2 with average UK rainfall can easily fill a 1000-litre tank. If a filter collector is used, this will provide a good store of clean water to keep a garden in good heart all year round. On larger buildings such as farms or stables, much higher capacities can be used to provide a large supply of water for livestock drinking, wash-down etc. Plastic tanks up to 30,000 litres are readily available.
The Impact Of Sunlight On Stored Water
Where water is exposed to sunlight for long periods, algae and various micro-organisms can develop and flourish, which can lead to the water becoming discoloured and smelly. This is far worse when leaves and other debris are allowed to accumulate within the tank, hence the importance of pre-tank filtration. Equally important is the need to exclude sunlight as much as possible. The solution is simply to ensure that above ground storage tanks are opaque and not open-topped. Fortunately the majority of such tanks are either black, brown or dark green. Temperature is another factor, and the cooler the water is kept, the ‘healthier’ it will be, so ideally site the tank in a shady spot or else provide some screening; this may be desirable anyway purely from an aesthetic point of view.
Overspill During Periods Of Heavy Rain
During rainy spells or prolonged downpours the tank will at some point fill to capacity and overflow. The tank must therefore have an effective overflow pipe that discharges excess water to a drain. This is normally very straightforward as there will be a drain gully located beneath the downpipe. It is important that the overflow pipe is no smaller than the pipe feeding water into the tank. With some types of filter collectors it is possible to let the tank overflow back through the filter directly into the downpipe.
Risk Of Frost Damage
Above ground tanks needs to be protected against freezing. Plastic tanks allow a degree of expansion, which will cater for ice forming, but prolonged and frequent freezing can cause damage long term. One solution is to simply drain down the tank during the winter months; fine if the water is only required for the garden during the growing season. Alternatively, the tank can be insulated. Either choose a pre-insulated model, available from some suppliers, or use some form of DIY arrangement. Obviously any exposed pipework will need to be insulated to prevent bursting.
Depending on the size of the above ground storage tanks, a domestic property may require local authority planning permission, while a commercial or industrial installation may have lighter regulatory restrictions. A water butt or normal sized tank would cause no problems but, if you have ambitious rainwater harvesting plans, it’s always best to double check with the planning section of your local authority. Should restrictions apply to the size of above ground tank you had planned, bear in mind that an option may be to utilise a number of smaller tanks, linked together in series with piping to drain any overspill from one to the next.
Where To Get Above Ground Tanks?
We supply a range of above ground tanks that are perfectly suited to rainwater harvesting for both commercial and residential systems of all sizes, from homes to apartment buildings. Read more on our website.
You can also download our free eBook Guide To Rainwater Harvesting Systems for a great deal more very useful information on all aspects of this highly environmentally friendly activity. Click here to claim your copy.