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

30 The Mayor’s draft water strategy
Three Valley’s Central water resource zone
at 181.6 litres and the lowest was metered
households in Sutton & East Surrey Water’s
East Surrey water resource zone at 137.7
litres per person per day.
2.9 Table 2.3 compares London’s individual water
use in 2004 with other western European
capitals 13 . London is shown as 100.
2.10 Water demand is not just about a growing
population. The number of occupants in a
household also influences individual water
use. Table 2.4 shows how individual water
use differs depending on the number of
people in a household in Thames Water’s
supply area. It shows that, in the context
of water use, the economies of scale favour
multiple occupancy households. This
conflicts with the trend towards smaller size
households in London.
2.11 Generally households with a meter use less
water than those without (see section 3.17).
Just over one in every five properties in
London has a water meter. This lags behind
much of the rest of the developed world
where metering is the norm. For instance
Australia, Austria, Denmark, Finland, France,
Germany, Japan and Switzerland already
have 100 per cent metering of single-family
houses 15 . As a result, companies providing
water to Londoners have limited data on
how much households are using in different
areas, and what factors influence that use.
Their ability to influence the household
use of water, and indeed their ability to
measure and manage their use, is low. It is
also in contrast to gas and electricity, where
householders have always paid for their use
by the volume used.
Balance of supply and demand
2.12 To avoid running out of water, or damaging
the environment by abstracting too much
water (for example, by reducing river flows
to a level where fish cannot survive), it is
essential to balance supply and demand.
During most years, including most summers
and dry periods, there is sufficient water
in the rivers Thames and Lee together with
groundwater to meet London’s needs.
However, during prolonged periods of low
rainfall, supplies are limited and drought
actions may be required. Typically it takes
two winters of below average rainfall to
necessitate drought actions. Winter rainfall
is particularly important because it is during
the winter that groundwater stores are filled
so that they can support river flows and
abstraction in the next spring and summer.
Water companies have both Water Resource
Management Plans for the long-term and
drought plans to manage supplies in times of
shortage.
2.13 Water Resources Management Plans set
out how each water company intends to
balance supply and demand, and how it
intends to provide sufficient water to meet
demand and protect the environment over
the next 25 years. Water companies update
their plans every five years, in line with the
price review process (see Chapter 6). Since
2007, these plans have been a statutory
requirement under the Water Act 2003,