28 March 2007
All public drinking water in the UK is disinfected before supply, usually by the addition of a chemical oxidant such as chlorine, chlorine dioxide or ozone and increasingly through the use of physical disinfectants such as ultraviolet (UV) light.
Summary
• UK water suppliers place the highest priority on assuring the quality of water provided to their customers.
• 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 this 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 through inadequate disinfection are much more significant and immediate than any theoretical and long-term risks 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 substances and, to a much lesser extent, substances made or used by man. 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 differences between one source of drinking water and another are the extent of treatment and monitoring needed. Public water supplies are closely controlled and monitored and in the UK the regulation of the public water supply is transparent and independent.
The WHO emphasises the paramount importance of maintaining the microbiological safety of water supplies at all times. For public water supplies and some bottled waters, disinfection has an important role in the multi-barrier approach to ensuring safe water. Consequently, all public drinking water in the UK is disinfected before supply, usually by the addition of a chemical oxidant such as chlorine, chlorine dioxide or ozone and increasingly through 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, these will be present at low levels. Water suppliers make every effort to minimise such reactions and to maintain concentrations of any by-products that are formed at levels well below WHO guidelines for drinking water quality and below levels set in 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 water-related topic. The consensus from all authorities is that research has not provided adequate evidence that chlorination of drinking water has adverse effects on health. In spite of this, the authorities, in conjunction with the water supply industry, take a precautionary approach to minimising any theoretical risks from chlorination.
Phill Mills
Director of Water Services
020 7344 1833
