This policy position statement (PPS) reviews the current UK
situation regarding the state and maintenance of the water
distribution infrastructure and provides an objective view on how
water suppliers should balance conflicting requirements to minimise
cost and manage the risk of asset failure.
CIWEM's position on drinking water supply infrastructure
- Water distribution infrastructure is essential in maintaining
an adequate high quality, continuous drinking water supply at a
pressure sufficient to serve modern appliances. Although occasional
interruptions may be unavoidable, the impact and duration of these
should be minimised. Although unseen, it is essential that the
distribution network is regarded as a critical component and that
this is understood by decision makers.
- It is essential that the UK's stock of distribution assets does
not deteriorate. Appropriate funding for maintenance of these
assets should be provided through the local water charges.
- These assets are likely to be required for an extensive length
of time, possibly centuries. Therefore depreciation accounting is
an inappropriate accounting approach for such assets. It should be
assumed that they will be required in perpetuity and their function
maintained at current or improved levels.
- CIWEM endorses the Common Framework approach to assessing
capital maintenance requirements on the water infrastructure. This
means that asset observations should be maintained and used to
develop models to predict future performance.
- CIWEM supports recent work by UK Water Industry Research
(UKWIR)1 to develop national data bases which collect
performance data for pipes. Further work should be carried out to
understand the drivers which affect pipe deterioration rates.
- CIWEM recognises that in some areas the pipe network has
deteriorated to an unacceptable level. In such cases additional
investment should be made to bring the pipes back to an acceptable
level. The level of this investment should be decided taking
financial factors into account but also balancing the social and
environmental impact of unplanned repairs and the level of leakage.
The effect of such mains renewal should be included in any water
- Capital investment and maintenance expenditure has significant
impact on the maintenance of water quality after the treatment
plant. CIWEM supports the Distribution Operation and Maintenance
Strategies (DOMS) approach proposed by the Drinking Water
Inspectorate (DWI)2 which documents the approach to
maintaining water quality and sets out monitoring policies and
trigger levels within individual water organisations.
- CIWEM supports the development of improved installation
techniques which would minimise future maintenance and replacement
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 97 countries include
scientists, engineers, ecologists and students.
The network of mains supplying properties in the UK with
drinking water is extensive, covering nearly 400,000 km. Much of it
is built of cast iron or the more recent grey and ductile iron and
some dates back to the 19th Century. The iron mains corrode both
internally and externally and this can lead to leaks and bursts as
well as water quality problems, particularly discoloured water.
DOMS will ensure that capital investment and operational activities
are carried out in such a way that will minimise risk for the
England and Wales
After privatisation in England and Wales, the planning and
management of water distribution system maintenance has focused on
two distinct but related areas:
- Maintenance of the structural integrity and hydraulic adequacy
of the network to ensure no overall deterioration in the numbers of
bursts, reported interruptions to supply, and properties subject to
- Maintenance aimed at improving water quality in identified
In the private water companies, the first area was funded as
capital maintenance through the quinquennial business planning
process. This requires water companies to submit business plans
every 5 years detailing amongst other things, their estimated costs
for maintaining the existing water distribution network. Until the
most recent price review in 2004 (PR04), this relied largely on a
historical assessment of serviceability and expenditure. The
development of the Capital Maintenance Planning Common Framework
prior to PR04 promoted the adoption of forward-looking risk-based
analyses, and has been fully endorsed by the Regulators and the
The water utilities in Scotland and Northern Ireland are not
privatised. Scottish Water works to a regulatory period of 4 years
and is attempting to address the deterioration in the
infrastructure through the shorter investment periods. In spite of
this, performance indicators for the Scottish pipe network are not
yet comparable with England and Wales.
The second area was addressed by the Water Industry Act, which
under section 19 allowed water companies in England and Wales to
develop plans to renovate water mains in areas that have
experienced water quality problems due to asset deterioration. The
water companies form a legal agreement with the DWI to achieve
compliance with water quality regulations by a certain date. These
agreements are called 'section 19 undertakings'. The maintenance
investment required to meet these undertakings was funded
separately via the price reviews and the improvement in water
quality was validated using Pre- and Post- Rehabilitation
With the completion of many of the water company section 19
programmes, attention needed to turn to the maintenance of water
quality. In the absence of further guidance, maintenance to ensure
no deterioration in water quality would come naturally within the
scope of the Common Framework planning approach. On the face of it,
there would appear to be no reason for further Regulatory
The DWI therefore developed the concept of DOMS which would
document each water company's approach to monitoring the
distribution system and deciding what interventions are required
and implementing these interventions.
Scotland and Northern Ireland
The renovation of the distribution system started rather later
in Scotland and Northern Ireland than in England and Wales and
extensive work is still being undertaken. Different regulatory
regimes apply, although the DOMS concept and the Capital
Maintenance Planning Common Framework have been adopted by the
Scottish Executive who provide the regulatory input in Scotland. In
Northern Ireland, where the water industry has recently been
restructured, a policy has yet to be developed.
The maintenance of the water distribution network is essential
for the maintenance of water quality, the continuity of supplies to
customers and the achievement of an appropriate level of leakage.
Establishment of this level of maintenance is not straight forward
as the assets are not visible. However, the taking of pipe samples
in order to develop mains deterioration models and newer
non-destructive techniques are improving the information available
to engineers all the time. The pooling of data amongst water
companies increases the robustness of such models and CIWEM
encourages and supports all such co-operation.
There is no one serviceability indicator relating to water
quality in the distribution system which will indicate that the
integrity of the water distribution system is being maintained from
a water quality point of view. Although the set of serviceability
indicators used by the Water Services Regulation Authority
(Ofwat)3 in England and Wales has been extended to
include iron pick up in the distribution system, it is essential
that water companies consider local conditions and modes of
deterioration to develop their own monitoring procedures.
The monitoring of water distribution networks is needed both to
ensure that day to day water quality is maintained and to identify
if the pipe condition has deteriorated in such a way that water
quality is jeopardised
Although mains failures (burst mains) are often regarded as a
structural problem, it should be recognised that any mains failure
introduces additional risk to water quality.
It should be recognised that there are a variety of approaches
to maintaining water quality integrity in a water distribution
system. A water supplier should examine all the alternatives
including operational (opex) and construction (capex) solutions and
select the approach which balances risk and expenditure to an
Much of the existing distribution system has been constructed
from iron. More recently, newer materials such as asbestos cement,
uPVC and polyethelene have been introduced. All materials in
contact with drinking water are subject to rigorous testing and
must be approved under Regulation 31 and 32 of the Drinking Water
(Quality) Regulations. CIWEM recommends that all pipeline materials
are approved under these regulations.
Different pipe materials have different lifetimes and it is
important for water utilities to invest at such a rate to maintain
the network as a whole and to ensure that it does not deteriorate
to such an extent that the number of repairs required either
reaches an unacceptable level or cannot keep pace with the outbreak
of new leaks. In particular research is still needed to understand
the lifespan of the newer materials such as polyethylene,
polyurethane and epoxy resin to ensure that replacement of new and
renovated pipes is carried out in an efficient and timely
It should be recognised that installation, repair and removal of
water mains can have a substantial impact on the environment, e.g.
through the noise from construction work, traffic delays creating
an additional pollution load, the need to dispose of excavated
material, or the requirement to replace excavated material with
suitable sub-grade and top coat which may require transportation of
quarried material. Even the pipe materials themselves use non
renewable materials such as hydrocarbons. As such CIWEM
endorses any moves which allow the provision and maintenance of
water mains to be carried out in a more sustainable way, and which
reduces the carbon footprint of such work.
Operational interventions in the distribution system are of key
importance in maintaining water quality. These include both
interventions which reduce water quality risk (e.g. mains flushing)
and those that pose a risk in themselves (e.g. valve operations)
Although both the common framework and the guidance letter MD161
issued by Ofwat in April 2000 emphasize the importance of
considering operational interventions, the objective of companies'
Common Framework analysis is the justification of capital
maintenance, taking into account potential trade offs between opex
and capex. In this context there is a risk that operational
interventions will be neglected, and there is no requirement to
apply similar approaches for practical maintenance planning outside
the context of a price review.
Certain mains, generally referred to as 'trunk' mains or
critical mains have a particularly high impact on water supplies if
they fail. A different approach should be used with these mains
with risk assessment based on factors known to affect pipeline
deterioration and where dictated by risk assessments, regular
inspection, particularly using the latest non-destructive
techniques. Valves on these mains should be regularly
exercised and maintained.
Note: CIWEM Policy Position Statements (PPS) represent 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, and that previously-held views may alter and lead
to revised PPS's.
1 UKWIR is an organisation for commissioning and
managing collaborative research on behalf of the UK water
2 The DWI is the regulatory organisation responsible for
ensuring that drinking water quality standards are maintained and
the legal obligations of water companies relating to drinking water
quality is met.
3 Ofwat is the economic regulator for water and sewerage
in England and Wales
Ofwat: MD 161, Maintaining Servicibility to Customers, April
UKWIR: DOMS Guidance Manual Volume 2: Guidance (06/WM/18/2)
UKWIR: Capital Maintenance Planning: A Common Framework
HMSO: Water Industry Act 1991
Statutory Instrument 2000 No. 3184: The Water Supply (Water
Quality) Regulations 2000