This policy position statement outlines the key issues
associated with loss of water from the distribution network between
the point of water treatment and delivery of water (potable and non
potable) to the customer. This loss of water is known colloquially
CIWEM's Position on Leakage:
1. All water supply distribution networks suffer some
leakage. Zero leakage is the ultimate goal. However it is generally
accepted that it is not, currently, technically possible, or indeed
economically viable, to achieve zero leakage. CIWEM recognises and
applauds the considerable reductions in leakage made by water
companies in recent years.
2. CIWEM recommends that the targets set for leakage
reduction by water utilities should take greater account of
environmental and social factors as well as economics.
3. CIWEM recognises that although some of the water lost
from buried water pipes does return to the environment, this may
not be to the same aquifer from which it was originally abstracted
and the treatment process may mean that the water chemistry of
potable water can be substantially different from that in the
aquifer to which it returns.
4. CIWEM recognises that a considerable amount of energy is
used to abstract, treat and pump potable water and as a result
leakage contributes to the carbon footprint of water supply.
5. CIWEM recognises that not all the leakage currently
reported is lost from pipelines owned by water utilities; around a
third to a quarter of total leakage is from customer owned supply
pipes. There are a number of options available to reduce the losses
from these privately owned pipes and CIWEM advocates further
studies to identify the best course of action.
6. CIWEM recommends that in the long term, all water use
should be metered for the purposes of water conservation and more
accurate leakage measurement.
7. CIWEM recommends that leakage should not be quoted in
terms of percentages as this is misleading. The most appropriate
units for quoting leakage are in l/property day or l/km
8. CIWEM supports an holistic approach to leakage control,
by considering the components of leakage and selection of
The Chartered Institution of Water and Environmental Management
(CIWEM) is the leading professional body for the people who plan,
protect and care for the environment and its resources, providing
educational opportunities, independent information to the public
and advice to government. Members in 98 countries include
scientists, engineers, ecologists and students.
Leakage is an important element in the supply-demand balance for
most water supply companies. In the recent past droughts have
exposed the vulnerability of some UK companies in maintaining
supplies such that the question of what levels of leakage should be
accepted has been raised by the media, the public and specialist
groups such as the All Party Parliamentary group for Water.
Currently water utilities set their own annual targets which are
agreed with the economic regulator OFWAT, based on achieving or
maintaining the sustainable economic level of leakage (SELL) . Most
companies have now reached SELL. OFWAT now assesses whether targets
have been passed or failed against a 36 month rolling average.
The high profile of leakage in the UK media and the visibility
of some leaks has led to a high level of public and customer
awareness. The profile of water utilities is, to a
significant degree, judged by their behaviour on leakage.
Generally, the UK water utilities are significantly better
than in many other countries, and the lowest leakage companies in
the UK compare well internationally.
Leakage levels are generally quoted in Ml/d which is the leakage
lost per day averaged over a year. Two additional leakage figures
are also quoted in OFWAT's annual report, litres lost per property
connected per day (l/prop/d) and litres lost per km of distribution
pipe owned by the company per hour (l/km/hr). These last two allow
some comparison between companies and it is generally recognised
that the l/prop/d is more appropriate for urban and semi-urban
contexts. In some countries leakage is still expressed as a
percentage. This is very misleading as leakage can vary with
consumption without any change in the actual leakage. A unit
proposed by the IWA Water Loss Task Force is the infrastructure
leakage index (ILI) which is a unitless figure based on actual
leakage compared with a theoretical minimum. Whilst this has some
use in international benchmarking the ILI does not take pressure
management in to account, does not consider the overall condition
of the pipes and due to the use of theoretical values, is not
suitable for regulatory targets.
There have been significant reductions of leakage achieved by UK
water companies in recent years. However what is not widely
recognised is that, if left unattended, leakage rises steadily.
Research demonstrates that there is a need for an increasing level
of resourcing to attain progressively lower leakage levels.
The primary components of leakage management are:
• water may be lost from all parts of the network;
• raw water mains to treatment works
• trunk mains to service reservoirs
• water utilities distribution pipes (including communication
• customer supply pipes
• in addition water may be lost from customer premises through
e.g. leaking supply pipes, dripping taps, faulty WC cisterns
The primary benefits of leakage reduction are seen as:
• reduced abstraction and therefore environmental
• increased reliability of water supplies
• deferment of capital expenditure on water resources and
• reduced operating costs (if above the ELL)
• improved public perception of water companies and
encouragement to conserve water themselves.
• reduced energy and chemicals for treatment and pumping
• reduced infrastructure damage (e.g. weakened road
Zero leakage is the ultimate goal. However it is not, currently,
technically viable, or indeed economically sound, to achieve zero
leakage. Although water lost from the distribution network will
return to the environment, it may not be available for abstraction,
it may be of a different water chemistry and as mentioned above, it
will have already required a substantial energy input which is then
Accurate estimation of leakage requires an estimate of the
volume of water delivered to customers in their properties.
However, with only some 15% of household supplies metered, direct
measurement has not yet been achieved. Leakage estimates are
therefore built upon components and statistical methods which
themselves are subject to potentially large errors in
Around a third to a quarter of total leakage is from customer
owned supply pipes which convey water onwards from the curtilage of
the property. Although water companies offer subsidised repair
and/or replacement schemes, this approach has clouded the matter of
responsibility and brought into the debate future ownership of
customer supply pipes.
Although there has been a substantial degree of research into
methods of determining current and future SELL, there is still
insufficient clarity as to the methodologies of deriving SELL, for
the short and longer term, for them to be agreed in the UK.
The evaluation of the long term SELL is dependent on the cost and
timing of other means of maintaining an adequate surplus of water
supply over demand, such as demand management and water resource
and supply enhancement. In undertaking a holistic approach to the
costs and benefits there is a requirement to include social as well
as environmental costs. There remains uncertainty as to the
factors to include and how to cost them.
To determine the level of leakage it is necessary to determine,
and then deduct, water which is being legitimately consumed.
However the majority of consumption in most cases remains
unmeasured and has to be estimated thus giving rise to uncertainty
in leakage estimates. The main source of error is seen, by the
regulators in particular, as the estimate of unmeasured per capita
consumption (PCC). There is a suspicion that companies reporting
high PCC may in fact have higher than reported leakage. At present
the most common way for water companies to estimate unmeasured
consumption is by measuring the consumption in detail for a small
sample of customers then use statistical methods to assess
consumption on a company wide basis.
In addition the lack of metering means that the level of leakage
on the privately owned 'supply pipe' is also difficult to
identify and assess. If there is no apparent impact on the property
or the supply of water it can be difficult to persuade the property
owner to repair the pipe, although many utilties now offer a
subsidized repair service.
Pipe pressures have now been shown to have a clear relation to
leakage, although there is still some disagreement about the degree
of reduction that a pressure management project will bring about,
and whether this reduction will gradually be eroded as the water
pipe deteriorates. Pressure control is now widespread in most water
companies. However, pressure can raise concerns about
availabilities of fire fighting water.
As pipes deteriorate there is a theoretical point at which the
cost of replacing the pipe is less than the ongoing cost of
repairimng leaks. However, this point may lead to an unacceptably
high level of interruptions in supply to certain customers.
Therefore any replacement programme must consider capital
investment costs, operational costs, environmental and social costs
for both repairs and placement as well as customer service.
CIWEM recognises the importance of leakage reduction in the
management of water supplies and its contribution to the
sustainable management of water resources. In this context it
supports the efforts of all stakeholders in the water industry to
manage leakage effectively and economically.
CIWEM is concerned, however, that because of the high political
and media interest in leakage, the role that future leakage
reduction can play in securing reliable water supplies may be
over-played in some parts of the UK. In particular it has little
impact on the ability to meet peak demand. In this respect there is
a requirement to communicate effectively the measurement of leakage
e.g. Ml/d etc, loss per km of pipe, or per head served, the
economics of leakage and how leakage targets are set and
CIWEM recognises the difficulties of quantifying the components
of SELL, especially the environment and social externalities. CIWEM
supports the recent initiatives to clarify how leakage targets
should be set and realises that all the interests need to be
balanced. The Institution does however believe that a long term
view needs to be taken which has due regard to the long term
protection of the water environment and the need to conserve and
make best use of water. These have to be addressed in the face of
the uncertainties of the impact of global warming, including its
effects on the availability of water resources and demand, and the
need to minimise waste from the use of chemicals and fossil fuels
to treat and distribute water.
In addition to the repair of leaks as they become apparent, it
is essential that a long term deterioration of the mains network is
not allowed to develop through inadequate rates of mains relining
and renewal. CIWEM notes from information published by OFWAT that
the implied average age of water mains before relining and
replacement is currently 60 years for the water utilities as a
whole, (based on the maintenance activity of companies in the
period 1990-91 to 1997-98). The most active company has mains with
an average asset life of 29 years and the least active 272 years.
CIWEM does not consider this range to be acceptable and considers
that best practice is likely to be closer to that achieved by the
most active company. CIWEM is aware of the costs to customers of
increased activity on mains renewal or relining, but believes that
customers should pay the full costs of service provision rather
than allow assets to deteriorate. It supports the approach detailed
in the UKWIR report 'A Common Framework for Capital
CIWEM takes the view that future leakage targets may be tighter
for some water utilities than those currently set in order to take
a long term view of the environmental and social issues, and in
recognition of the levels achievable by the best performing
companies. However there needs to be recognition of the
practicalities of meeting these targets, the uncertainties in the
analytical models and the practicalities of leakage measurement. In
addition it is important that a rate of mains renewal is funded
which ensures that leakage levels in the future can be controlled
at economic levels.
Leakage practitioners currently exchange information through the
Water UK Leakage Network and through professional activities
initiated by professional organisations such as CIWEM. It is
essential that the continued co-operation of leakage professionals
be promoted and supported and that comparative or actual
competition does not obstruct this activity.
CIWEM also endorses the general principle of EC environmental
legislation of 'no deterioration' which should be applied to
leakage targets and that once leakage has been reduced it should
not be allowed to subsequently rise. The approach of monitoring
rolling averages is sensible to ensure that any exceptional weather
conditions do not lead to inappropriate regulatory action.
CIWEM considers that Government should give the economic
regulator (OFWAT) guidance on the targets which should to be set
for companies so as to ensure that wider social, environmental and
practical issues are taken into account. However Government will
need to be advised by experts in the industry in doing so. In
addition CIWEM supports the use of targets which are not misleading
and can be easily understood, e.g. Ml/d, l/prop/day or l/km/hr
rather than percentages.
CIWEM supports the introduction of pressure management systems
where these are shown to be cost effective as this ensures a
consistent standard of service to customers throughout the day.
However, it is recognised that discussion with all customers,
including the fire service, is required before the introduction of
any new management scheme.
CIWEM recognises that there are several mechanisms by which
leakage can be reduced, such as by pressure reduction, district
metering and associated programmes of active leakage control, and
online monitoring, "find and fix" and leakage helplines. All such
measures should be pursued to their economic level and best
practice developed and shared amongst water undertakers.
Note:- CIWEM Policy Position Statements (PPS) represents the
Institution's views on issues at a particular point in time.
It is accepted that situations change as research provides new
evidence. It should be understood, therefore, that CIWEM
PPS's are under constant review, that previously held views may
alter and lead to revised PPS's
That part of the service pipe which is not the communication pipe
and is owned by the property owner whose premises are supplied by
That part of the service pipe which is owned by the Water Company
and laid in the same street as the main to which it is
Pipe connection between a water main and the premises being
supplied. The Service pipe includes accessories such as the
ferrule, boundary box/stopcock or other apparatus.
WRc. 2009. 'Code of Practice for the Self Laying of Water Mains
and Services - England and Wales' WRc Swindon UK
OFWAT. 2002. Tripartite 'Best Practice Principles in the
Economic Level of Leakage Calculation
UKWIR. 1999. NERA The environmental and social value of leakage
WRc. 2008. Leakage Target Setting - A Frontier Approach WRc
OFWAT. 2007. RPS Providing Best Practice Guidance on the
inclusions of Externalities in the ELL Calculation
(Main Report and Guidance)
UKWIR. 2002. Capital Maintenance Planning: A Common