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Chartered Institution of Water and
Environmental Management (CIWEM)

106-109 Saffron Hill, London, EC1N 8QS  
Tel: 020 7831 3110   Fax: 020 7405 4967

Drinking Water Supply Infrastructure Management


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 management:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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 resource planning.
  7. 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.
  8. CIWEM supports the development of improved installation techniques which would minimise future maintenance and replacement costs.

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 optimum expenditure.

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:

  1. 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 low pressure.
  2. Maintenance aimed at improving water quality in identified problem areas.

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 water companies.

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 Assessment (PPRA).

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 intervention.

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 acceptable degree.

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 manner.

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.

September 2008

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 industry.
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 2000 

UKWIR: DOMS Guidance Manual Volume 2: Guidance (06/WM/18/2)

UKWIR: Capital Maintenance Planning: A Common Framework (02/RG/05/3)

HMSO: Water Industry Act 1991

Statutory Instrument 2000 No. 3184: The Water Supply (Water Quality) Regulations 2000


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Chartered Institution of Water and
Environmental Management (CIWEM)

106-109 Saffron Hill, London, EC1N 8QS  
Tel: 020 7831 3110   Fax: 020 7405 4967