The Mayor's draft water strategy - london.gov.uk - Greater London ...

42 The Mayor’s draft water strategy
which it would cost more to reduce leakage
further than it would be to produce more
water from existing or alternative sources.
3.5 The procedure for calculating the ELL has
been revised and is now more sensitive
to costs and benefits including social and
environmental costs 26 . Ofwat now uses
the term ‘sustainable economic level of
leakage’ (SELL) to reflect this. Whilst there
is a good general understanding of the
social and environmental costs of action
to control leakage (for example, traffic
congestion due to mains replacement or
repair), the estimates of the environmental
benefits (such as reduced abstraction and
carbon emissions) are less clear. However,
in the London context, there are serious
omissions. For example, no account is taken
of the potentially serious damage caused
to other infrastructure such as the London
Underground network by leaks and burst
mains 27 . A recent study shows that there is
very little information available to assess
the costs of disruption and loss of business
caused by leaks and burst mains 28 .
3.6 The Environment Agency has identified
much of London’s water resources as ‘overabstracted’
(see paragraph 2.29), and the
Water Framework Directive will require
measures to address this. The Mayor
expects that the current price review will
take a longer-term sustainable approach
to London’s water infrastructure. There
is further discussion of ELL in Chapter 6
Paying for water.
3.7 Leakage has two elements; the volume of
water lost through leaks on the distribution
mains network (referred to as distribution
losses) and the amount lost from customers’
supply pipes (referred to as supply pipe
losses). In meeting their economic level of
leakage targets, water companies are:
• replacing old leaky distribution mains
• lowering the water pressure in the
distribution network
• finding and fixing leaks on their
distribution mains
• repairing leaks on their customers’ supply
pipes.
Replacing water mains
3.8 Many of London’s water mains are over 100
years old. But it is not just the age of the
pipes that leads to high leakage levels. The
soil can affect the pipes buried within it in
two ways: through corrosion (which causes
pitting and structural weakness) and through
movement of the soil that puts stress on the
pipes and their joints. Research shows that
London has a significantly higher proportion
of corrosive soils than other parts of the
country. Also, London’s clay soils are more
susceptible to soil movements due to the
changes in the soil moisture. Inner London,
served by Thames Water, generally suffers
the worst problems.
3.9 As part of the 2004 price review (see
Chapter 6 for an explanation of the price
review process) Ofwat set Thames Water
strict leakage reduction targets. In order
to meet these, the company embarked on
a major leakage reduction programme and