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Water UK technical briefing note: disinfection by-products WATER UK BRIEFING NOTE DISINFECTION BY-PRODUCTS SUMMARY UK water suppliers place the highest priority on assuring the quality of water provided to consumers The World Health Organization (WHO) has emphasised the importance of a safe, sustainable and affordable supply of drinking water as close to the point of use as possible and that the effectiveness of disinfection should never be compromised with primary consideration given to ensuring microbial quality. Water UK strongly endorses such a view. All natural waters contain substances occurring in the environment. Some of these are beneficial to health, some are of no significance and some may be hazardous to health if present in sufficient quantities. Public drinking water supplies in the UK are closely regulated and monitored to ensure the quality and safety of the water supplied and safety is open to public scrutiny. The risks to health from inadequate disinfection are much more significant and immediate than any theoretical and long-term risk from by-products of the disinfection process. Water UK supports the WHO position regarding both the need for appropriate disinfection and the importance of supplying safe drinking water to the tap. TECHNICAL BACKGROUND All water contains both natural and, to a much lesser extent, substances made or used by man. WHO and other United Nations Authorities emphasise that one of the most important requirements of any society is a safe, sustainable and affordable drinking water supply that is available as close to the point of use as possible. All waters from natural sources contain micro-organisms and chemicals that are part of the natural environment through which the water passes. Some of these are potentially beneficial to health, some are of no significance and others are of concern for health, if present in sufficiently large quantities. Water may also contain substances that are present as a consequence of use by man. Some are natural and some are man-made. This is true of all waters. The main difference between different sources of drinking water is in the extent of treatment and of monitoring. Public water supplies are closely controlled and monitored and, in the UK, the regulation of the public water supply is transparent and independent and the quality is open to public scrutiny. January 2007 Water UK technical briefing note: disinfection by-products WHO stresses the paramount importance of maintaining the microbiological safety of water supplies at all times. For public water supplies and some bottled waters, disinfection is an important barrier in the multi-barrier approach to ensuring safe water. Consequently, all public drinking water in the UK is disinfected before supply, usually by addition of a chemical oxidant such as chlorine, chlorine dioxide or ozone, and increasingly by the use of physical disinfectants such as UV light. Although oxidants can react with naturally occurring organic and inorganic matter in the water to form a range of by-products that are present at low levels, water suppliers make every effort to minimise these reactions and to maintain concentrations of any that are formed well below the levels set in the World Health Organization guidelines for drinking water quality and below any European or UK standards. These levels are set on the basis of safety and are considered to be highly conservative. The most commonly used disinfectant is chlorine because it is effective and easy to control. Chlorination and its safety has been the subject of a huge amount of research, probably more than any other single topic, and the consensus from all credible authorities is that all of this research does not provide adequate evidence that chlorination of drinking water causes health effects. In spite of this, the authorities, in conjunction with the water supply industry, takes a precautionary approach to minimising any theoretical risks from chlorination. There are many myths regarding the presence of substances in drinking water both in public water supplies and bottled waters. These are largely based on half-truths or misunderstanding and some are associated with advertising commercial products. In the UK we are fortunate in having safe, high quality drinking water available from a number of sources including the public water supply. January 2007