Low Energy House

Low Energy House - Grey Water Systems - Water Collection

Typical grey water systems collect waste water from baths, showers and washbasins. The water is then treated and stored until it is required for toilet flushing and garden watering

Grey Water Systems

Rainstore Above Ground Tank - Image Provided by Kingspan Water RangeGrey water is water that was previously supplied as ‘wholesome water’ but which has been used in washbasins, baths and showers.

Before deciding on a grey water system, it is important to calculate how much grey water is likely to be generated from washbasins, baths and showers compared with the likely demand for toilet flushes and garden irrigation. It is then possible to calculate the potential savings from reduced water consumption set against the costs of installation and maintenance.

Grey Water Collection

In order to collect and distribute the grey water, a separate internal waste water drainage system must be fitted.  The water is stored in a tank from where a distribution system takes it, by a pump or gravity, to the toilets and/or garden tap.  A mains fed back-up system will be necessary for times when supply of grey water does not meet demand. Equally, an overflow system connected to the sewer will be required when grey water exceeds demand.

Grey Water Systems - Treatment

The method and standard of treatment in a grey water system will vary with the size of the system. Larger grey water systems that supply more than one property tend to use more sophisticated treatment methods than smaller, individual collection systems.

Grey Water Collection and Storage SystemGrey water treatment can be classified as ‘physical’ or ‘biological’.

  • Physical treatment is common in small scale collection systems and usually consists of a basic filtration process. A simple filter is required to remove any large solid particles.
  • Biological treatment is generally used in larger collection systems and works in a similar way to the processes used at a sewage treatment works.

Some collection systems use a combination of the two methods; this is called ‘bio-mechanical treatment.

Basic physical collection systems generally use disinfectants to stop the growth of bacteria while the water is in storage.

Saving Money with Grey Water Systems

Re-using waste water reduces drinking water and waste water costs. This re-use of water reduces the load on valuable ground water reserves as well as reducing the drainage burden. Grey water systems have the potential to save a third of domestic mains water usage.

Grey Water Systems - Cost

Installing a grey water system for use in an individual property can be expensive.  A typical off-the-shelf single house domestic collection system may cost in excess of £3,000 to purchase.  This system will also incur running and installation costs. Grey water systems that are installed in new buildings are usually more cost effective than those retro-fitted into existing properties. Communal grey water systems are generally more cost effective than those installed in single properties.

Grey Water Systems - Water Meters

Most UK residents pay their water and sewerage charges based on the rateable value of their home. In order to save money on water supply, it is necessary to contact the water company and arrange to have a water meter fitted. Financial savings will depend on the price of the water in the area and the volume of water used.

Grey Water Systems- Prevent Contamination of the Mains Supply

Under the Water Supply (Water Fittings) Regulations 1999, various degrees of precaution must be taken against possible contamination of the mains drinking water. Pipes and supply points on the grey water system must be clearly labelled in order to avoid confusion with the mains drinking water.

Rainwater Harvesting

For information on Rainwater Harvesting Link to - Rainwater Harvesting

It is advisable to take simple water conservation measures before investing money in a grey water system

Grey Water Systems can save up to eighteen thousand litres of fresh water a year for each person.  This represents 33 per cent of daily household water use