Select Committee on Public Accounts Thirtieth Report

1  Responsibilities for preventing sewer flooding

1. Sewer flooding is among the worst service failures a householder can suffer, with raw sewage flooding into homes, gardens or business premises. There are four main causes of sewer flooding: hydraulic overload, when the capacity of a sewer is insufficient for the volume of waste water flowing through it; blockages, when the flow in a sewer is impeded; the collapse of the sewer itself; and equipment failure, when the machinery driving the flow in the sewer, such as a pumping station, breaks down. Figure 1 shows the main causes of flooding of the interior of homes and business premises.

Figure 1: Causes of internal sewer flooding incidents
Cause Percentage of incidents
Hydraulic overload (insufficient sewer capacity) 45
Blockages 45
Sewer collapses5
Equipment failure 5

Source: C&AG's Report, Figure 3

2. Sewers are open networks. They are designed to collect waste water from homes and business premises. But they can also collect it from highways, car parks and other urban areas, and discharge waste water to rivers and the sea as well as sewage treatment works. Although newer parts of the sewer network separate storm drainage from the sewer system, the majority of the system remains a combined system in which rain water combines with waste water from properties.[3]

3. The combined nature of the system means that there are a variety of organisations with direct or indirect responsibility for preventing sewer flooding. These include the 10 water and sewerage companies in England and Wales; local authorities who are responsible for local highways, and granting planning permission for new developments which connect to the system; the Highways Agency; and the construction industry. In addition, the Environment Agency has responsibility for setting maximum acceptable limits of discharge from the sewer networks into rivers and the sea. And the Department for Environment, Food and Rural Affairs (the Department) has general responsibilities for changes to the regulatory framework, setting new standards, and promoting new legislation for the water and sewerage sector.[4]

4. The range of bodies involved in managing and connecting to the sewer networks can mean that when a householder suffers from sewer flooding, it may not be clear who is responsible for causing the incident and preventing similar incidents in future. From the customer's point of view, it can seem as though everybody is blaming each other: the local authority is blamed for not clearing the gulleys by the side of road; the housing developer is blamed for building houses in the wrong place; and neighbours can be blamed for things they have or have not done.[5]

5. The sewer network assets are the responsibility of the 10 water and sewerage companies.[6] Each company has a monopoly in its region. Ofwat's role under the Water Industry Act is to ensure that the companies fulfil their duties as sewerage undertakers. It does not take operational decisions on the size and shape of the network, and it can only compel companies to undertake specific works through an enforcement order. Ofwat has not taken enforcement action against any company in relation to its sewerage service because it has found its discussions with companies have led to action plans which have dealt with emerging problems.[7]

6. Ofwat's main tool for ensuring that companies fulfil their duties is the price control and associated conditions it places on them as monopolies. The price control covers a five year period, with the current period ending in March 2005. At the start of every price control period, Ofwat sets the outputs that the water companies must deliver in return for the agreed price limits. Ofwat then monitors each company's performance against key performance measures. [8]

7. For sewer flooding, the main performance measures are the number of properties flooded and properties at risk of sewer flooding.[9] The annual performance of the industry against these two measures is shown in Figures 2 and 3. The figures show that the number of properties flooded internally shows no clear pattern, but varies between around 5,000 to 7,000 properties each year, and the number of properties at risk of sewer flooding has fallen from just over 30,000 to 11,600 in 2002-03.

Figure 2: The number of reported internal sewer flooding incidents

Source: Ofwat Annual Levels of Service reports

Figure 3: Properties at high risk of sewer flooding

Source: C&AG's Report, Figure 5

8. There are doubts about the reliability of this information. For sewer flooding incidents, it is possible that some incidents are not reported by householders because they fear blighting their property. Ofwat said that this was one of the factors which meant that less serious flooding events, such as sewage at the bottom of the garden, are not reported regularly.[10] In addition, the wide range of methods used to estimate the number of properties at risk means that there is inconsistency between the figures quoted by different companies. Ofwat did not seek complete uniformity in the way companies prepared at-risk registers, as there should not be too much discrepancy between them, but it would be looking for greater consistency between the registers in future.[11]

9. Figure 3 shows a large fall in the number of properties at risk between 2000-01 and 2001-02. This fall is the result of the reclassification of 10,000 properties by Thames Water because these properties had not flooded in the last ten years.[12] Ofwat confirmed that the water industry could not take credit for the substantial dip in the figures between 2000 and 2002.[13] The reclassification demonstrates the difficulties of obtaining reliable, consistent data on properties at risk.

10. One factor causing sewer flooding is new housing development. New developments may mean that a sewer system which was adequate when it was designed becomes subject to intolerable strain. Ofwat explained that new developments had an almost absolute right to connect to the network, and whether this absolute right should continue was a significant issue.[14] Water companies did not have a formal role in the process for approving new planning applications and perhaps water companies should be made statutory consultees as part of the planning process.[15]

11. As Figure 1 shows 45% of sewer flooding incidents are caused by blockages. Many of these result from households and business, such as restaurants, putting inappropriate items, including fat and nappies, down their drains.[16] They are therefore preventable. Ofwat are responsible for ensuring that water companies fulfil their duty to promote the efficient use of water by their customers.[17] There is no equivalent duty to promote the effective use of the sewerage system. But it may be in companies' interests to educate consumers on the risks of putting the wrong things down the drain, since it could reduce the number and severity of blockages. Ofwat had not explored the case for water companies conducting education campaigns. It would, however, take companies' proposed education programmes into account when setting five-year price limits.[18]

3   Q 36 Back

4   C&AG's Report, para 1.7 Back

5   Q 28 Back

6   Q 3 Back

7   C&AG's Report, para 2.14 Back

8   50th Report from the Committee of Public Accounts, Pipes and wires (HC 831, Session 2001-02) Back

9   C&AG's Report, para 1.17 Back

10   Q 23 Back

11   Qq 47, 49 Back

12   C&AG's Report, para 1.21 Back

13   Q 31 Back

14   Q 21 Back

15   Q 22 Back

16   Qq 40-42 Back

17   8th Report from the Committee of Public Accounts, Office of Water Services (Ofwat): Leakage and water efficiency (HC 397, Session 2001-02) Back

18   Q 42 Back

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