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

flushing, clothes washing and outdoor
use without further treatment. Table 3.5
sets out possible acceptable water quality
properties for different applications. BSI is
Case study | Roppongi Hills, Tokyo
Whilst the use of reclaimed water, both
rainwater and grey water, is regarded as novel
in London and the UK, it has been used for
many years in other cities such as Tokyo
where it is regarded as routine. Sumida Ward
(equivalent of a London borough) has been
promoting rainwater harvesting since 1984 and
now requires all new buildings with a site area
of more than 500 m 2 to install such systems.
Tokyo Metropolitan Government applies a less
stringent standard across the whole of the
city, requiring new buildings with a floor area
of more than 10,000 m 2 to install rainwater-
harvesting systems.
Grey water reuse is also well established. A
notable example of the integration of rainwater
harvesting with grey water reuse is the
Roppongi Hills development in central Tokyo.
The filtration plant is illustrated here. This is
mixed use redevelopment integrating office,
residential, hotel, retail, and cultural functions
with parks and plazas. The project, covering
approximately 11 hectares, with a total floor
area of 724,000 m 2 , is one of the largest
redevelopment projects in Japan.
Reclaimed water (16 per cent rain water and
27 per cent grey water) meets 43 per cent
looking at developing a British Standard for
rainwater harvesting systems and UKRHA
(UK Rainwater Harvesting Association)
is currently working on a rainwater Code
of demand in the building complex. The
developer, Mori Building Co. Ltd., has many
years of experience in building and operating
such systems in its developments having
installed the first grey water reuse system
in the Toranomon 37 building in 1981. They
estimate that reclaimed water systems add as
little as one per cent to construction costs.
Clearly, design expertise, engineering
capability and operating standards are
available internationally for the satisfactory
operation of water reclamation systems.
London needs to move towards incorporating
such systems in large new developments in
the city in order both to stem the growth in
water demand and to minimise discharges to
the sewer system.
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