Download Water UK technical briefing note: disinfection by

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