Rainwater harvesting in the UK

Rainwater harvesting in the UK. Within the UK garden water butts are commonly used to harvest rainwater from roofspaces. This water is used for gardening by filling watering cans. There is a growing demand for larger tank systems collecting between 1000-7500 litres of water. There are two main uses for harvested rainwater- garden usage for plant irrigation and domestic usage for flushing toilets and running washing machines. Water is almost always collected only from roof space, heavily filtered using either a filter attached to the down pipe, a fine basket filter or for more expensive systems, self cleaning filter placed in an underground tank.
Storage
Below ground tanks
Larger systems often use below ground tanks, the advantages of this include;
* Large tanks do not take up room or ruin aesthetic appeal of a garden.
* Water stays at a cool, constant temperature underground and there us no exposure to sunlight- this makes bacterial action very unlikely, leaving the water clear and oderless.
* Underground the systems are frost protected, so do not need to be emptied when freezing temperatures occour.
Above ground tanks
Large, above ground tanks are best used when water will be used quickly, for example on farms with a large water demand. Leaving the water in above ground tanks exposed to heat and light for elongated periods of time can encourage bacterial growth, discolouration and even a health risks.
Delivery methods
Three distinct methods are used to deliver water. All involve pressure sensitive electrical pumps.
Direct feed
The simplest system to install and often the least expensive to purchase. A pump is submersed within the outside tank. As the pump is pressure sensitive, the pump operates whenever a pressure drop is registered. For example when a garden tap is opened, or when a toilet is flushed the pump will start. The pump will switch off when the pressure builds up again within the pipe.
If the systems are being used for domestic use, a mains backup device must be installed. This activates should water in the outside tank rach a chritical level. The device usually uses a soloinoid valve attached to a mains water supply. A floatswitch within the tank detects when water supplies are depleated, mains water is delivered into the tank.
Rain management units
Rain management units are widely used within Europe in countries such as Germany. The systems are large, wall mounted units containing a non-submersible pump. The system works on a similar principle to a direct feed system, except the water is drawn from the tank into the house. Systems such as this are less common in the UK as they are better situated in houses with basement space as the system makes noise due to the pump whenever water is drawn.
Header tank systems
Many systems in the UK work by pumping water up to a header tank than gravity feeding appliences such as toilets and washing machines. There are vast benefits to this as should there be a powercut or pump failer the header tank will over ride to mainswater- so toilets will always flush. Many header tank systems use considerably less energy as the pump does not run every time an applience is used. Electronic level sensors within the header tank mean the pump only runs when the header tank is compleatly empty.
Rainwater Harvesting for drinking water
Due to the readily accessible drinking water supplies compared to some less developed nations, harvested rainwater is rarely used for drinking in the UK. As the water is classed as non potable, the water must be treated and tested, sometimes leading to a costly process compared to using mains water due to comparitvly low volumes using economies of scale principle.
Systems such as using UV filtration and reverse osmosis are available for areas where mains water is unavailable.

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