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The distribution of municipal water is a very major source of wastage.
All such distribution systems leak, with losses ranging from typically 3 to
10 per cent in most continental European countries. In some cases, losses in
Cyprus and elsewhere have been reported of over 25 per cent. The major cause
of these losses is the use of iron or reinforced cement pipes with
overlapping joints which are sealed with tow. In time, the vibration of
traffic, minor seismic activity and expansion and contraction from seasonal
water temperature variations will create sufficient movement that the seals
are no longer watertight. Even worse, glazed terra cotta pipes are also
porous, where the glazing has been damaged: they are also provided in
shorter lengths, so that there are more joints per kilometre. Flanged cast
iron pipes have gaskets that deteriorate with time and conditions and the
pipes themselves can break or rust through. Smaller leaks from underground
pipes can pass undetected for years, wasting thousands of tonnes of water.
Instruments are available for leak detection, either through measured
pressure loss under given conditions or acoustically. Deep soil conductivity
is also sometimes used.
For the anecdote, a leak from a cast iron pipe had washed away the soil
under a road in a Swiss city. It is estimated to have been leaking for over
five years. It was discovered only when the road collapsed under a 28 tonne
articulated truck. The resultant hole completely swallowed up the truck and
its trailer. It is estimated that over 200 m3
of soil had been washed away through storm channels.
There is an additional danger: sewage pipes are no less insecure and
leaks of raw sewage occur all too often. If a potable water pipe should
develop a leak in the same area, it is possible for microorganisms to be
drawn into the drinking water by the Bernouilli effect.
Ideally, all new underground water distribution systems should be made
from welded plastic pipes of suitable quality and which would have a typical
leak-free lifetime of more than 25 years.
Conservation
It is strongly recommended that all existing pipework dating from more
than 10 – 15 years be replaced as rapidly as possible. The cost of this will
not be negligible but the savings in water could amount to more than 10,000
tonnes per day, which is far from negligible. There exists a technology
which could provide a temporary palliative for the longer stretches of pipe
which are particularly leaky and which is neither very costly in materials
nor expensive to install. This consists of accessing the pipe through a
manhole or a pit every hundred metres. A polyethylene tubing of the same
diameter as the inside of the pipe is introduced and the water pressure
forces the tubing against the walls of the pipe for the length of the
stretch. Obviously, this can only be applied where there is no branching. In
places where this system has been installed, it is claimed that leaks have
been reduced by over 90 per cent at relatively little cost and with
relatively short interruptions of the water supply. Nevertheless, it is
emphasised that this method is suitable only as a temporary stop-gap,
typically for a maximum of two or three years, while new pipelines are
installed.
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