Guide to Part G of the Building Regulations: Sanitation, hot water safety and water efficiency: 2010 edition by Nick Price is an essential reference handbook to understanding the new and substantially updated 2010 Approved Document G, which came into force in April 2010.

In this exclusive extract, we look at the requirements for the supply of wholesome water.

'Wholesome' water is fit to use for drinking, cooking, food preparation or washing without any potential danger to human health by meeting the requirements of regulations made under Section 67 (Standards of Wholesomeness) of the Water Act 1991. These stipulate the criteria that the water must meet in order to protect the lifelong health of the population. These parameters include limits on:

  • Biological quality (including levels of bacteria and oocysts)
  • Chemical quality (including levels of metals, solvents, pesticides and hydrocarbons)
  • Physical qualities (including colour, taste and odour).

The quality of water that is supplied through public water mains is strictly controlled by legislation to ensure that it is wholesome, and is also subject to regular testing at the consumer's tap to prevent any loss of quality during transmission and storage.

Water that is supplied from private sources is subject to similar quality requirements and therefore is also considered to be wholesome. Within premises, water systems are subject to Water Regulations in order to prevent contamination of the water once it has left the water supplier's mains.

G1 lists those applications for which wholesome water must be supplied:

  • Drinking
  • Food preparation.

In very hard water areas, ion exchange water softeners can increase sodium levels above the permitted limit for wholesome water (200 mg Na/ litre). Because of the potential health implications to infants, and people on a low-salt diet or with other medical conditions, this water should not be used for drinking or food preparation. However, G1 considers softened wholesome water to be suitable for washing (i.e. washbasins, baths, showers and bidets) or for toilet and urinal flushing as an alternative to wholesome water. This is consistent with the Water Regulations Guide, which advises that a water softener should be fitted after the draw-off to a drinking water tap.

For some purposes, for example toilet flushing, water that is less than wholesome can be used. The quality of the water that can be used is dependent upon its end use, and therefore the appropriate quality needs to be assessed on the basis of risk. For example, water used for toilet flushing can be of relatively poor quality, as there is negligible personal contact with the water and the water in the WC bowl is already contaminated. Similarly, the quality of water used for garden watering with a watering can does not need to be high, but consideration should be given to water quality where plants for human consumption are grown. On the other hand, water that could come into contact with people, either directly or as an aerosol, presents a higher risk and therefore needs to be of better quality; for example, water delivered by high-pressure hoses used for vehicle washing, as well as potentially contaminating people, will give off an aerosol, and so presents a significant risk of Legionella. It should be noted that because larger systems have the potential to affect the health of a greater number of people, they should incorporate greater protection than that for a single dwelling.

There is some debate as to whether or not the water used for washing clothes needs to be wholesome. Recent research in Australia indicates that highly treated recycled water (intended for machine washing of clothes) will not lead to the transmission of micro-organisms in numbers likely to cause enteric diseases.

Alternative sources of non-wholesome include:

  • Groundwater abstracted from boreholes, wells or springs
  • Surface water from watercourses (e.g. streams, brooks, rivers) or ponds and lakes
  • Rainwater (generally collected and stored, referred to as 'harvested rainwater')
  • Greywater (i.e. wastewater from baths, basins and showers)
  • Treated wastewater (from sewage treatment plants or industrial processes).

The quality of the water from each of these sources will be different, and even from a single source will vary over time.

If an alternative water source is being considered, its reliability to provide the necessary quantity of water should also be assessed. Where the quantity cannot be guaranteed (excluding exceptional events, as even water mains can burst and cause cuts), a back-up supply will be needed. If the back-up supply is from a wholesome water source, there must be no possibility of contamination of the wholesome water supply by nonwholesome water (by strict compliance with the Water Regulations).

It is essential that non-wholesome water is not inadvertently supplied instead of wholesome water nor allowed to contaminate wholesome water systems. Prevention of contamination can be assured by compliance with the Water Regulations. (It should be noted that water can be drawn into wholesome water systems by partial vacuums, even being sucked through the air where there is an insufficient gap between the water and the pipework.) Inadvertent mis-connections can be avoided by clear and unambiguous marking of non-wholesome pipes and cisterns; using different types of pipework for wholesome and alternative water systems can also help to avoid mis-connections (e.g. copper for wholesome and plastics for non-wholesome), but marking is still essential, especially if the pipes are insulated. It should be noted that there are standard colours for different services (e.g. yellow for gas), with blue being assigned to water mains, so blue pipes should not be used for non-wholesome water.

Inside dwellings, labels should be used to identify non-wholesome pipework. Labels should be:

  • Green in accordance with BS 4800:1989 colour 12 D 45
  • Not less than 100mm long
  • Marked 'NON-WHOLESOME WATER' in black letters not less than 5mm high (note that other guides recommend different wording, such as 'Reclaimed water', 'Non-potable water' or 'Rainwater' – any term may be used provided that the message is clear)
  • Self-adhesive, wrap-around or mechanically fixed to the pipe at intervals not greater than 500mm and at key connection points.

For large-scale reclaimed water pipelines (e.g. multi-occupancy buildings, schools, offices) and where the pipes are insulated, marking in accordance with the principles of BS 1710 should be used.

Points of use should also be clearly identified by a label stating 'Nonwholesome water' or by a prohibition sign.

If, after a risk assessment, an alternative source of water is used, it is essential that the system is properly inspected and maintained so that it continues to supply the quality and quantity of water as intended. These routine checks should include:

  • Sources (e.g. check that there is no obvious contamination of the source)
  • Storage systems (check for contamination, e.g. a dead bird, in the storage cistern)
  • Filters (e.g. that they are not blocked or holed)
  • Treatment (e.g. by checking water quality)
  • Pumps (e.g. check electrical safety)
  • Distribution pipework (e.g. check that there are no leaks or misconnections).

Further details of rainwater harvesting systems are given in BS 8515:2009. Other British Standards are in preparation covering re-use of effluent from wastewater treatment plants and greywater re-use system.

About this article

Extract from Guide to Part G of the Building Regulations: Sanitation, hot water safety and water efficiency: 2010 edition externallink

To order a copy of this book, please visit RIBA Bookshops externallink.

Copyright RIBA Publishing June 2010.

Available to buy from RIBA Bookshops

Approved Document G: Sanitation, Hot Water and Water Efficiency: (2010 Edition) externallink

NBS Building Regulations externallink