Fresh Drinking Water - Stadtwerke Düsseldorf AG

Fresh
drinking
water round
the clock

Water –
Essence
of Life
From time immemorial mankind’s
destiny has been closely
linked with water. Civilised
races and empires thrived in
those climes where water was
available. Even nowadays
those regions with a balanced
water supply continue to be
in a more favourable position
than those with little water
or arid regions: industrialization
and the quality of life
clearly depend on the availability
of clean water, and the
latter is by no means evenly
distributed over the globe.
Daily per capita consumption
of drinking water in Germany
is some 128 litres – in contrast,
a family of six in
Ethiopia has a mere 16 litres
at its disposal, and is compelled
to undertake a twohour
walk, carrying the water
home in jerry cans. Only 20%
of all households in the world
are connected up to a central
water system, which is available
as a matter of course to
ourselves.

What is so unique about this
unexceptional substance
“water”?
From a purely chemical
point-of-view water is a
molecule from hydrogen and
oxygen with the formula
H O. This molecule has two
2
poles, that is a positive
partial-charge in the case of
hydrogen and a negative
partial-charge in the case
of oxygen. This so-named
“dipole formation” is
responsible for many of
water’s characteristics.
Water is an element, which
exists in nature in three
different forms, the states
of aggregation: as a solid,
a fluid and a gas.
Water is the only fluid
which expands when its
temperature drops. Its maximum
density is attained at
+4° Celsius.
The fact that the density of
ice is less than its fluid form
is known as the “density
anomaly”.
Thus water is heavier than
ice. If this were not the case,
water in its various forms
would freeze from the bottom
upwards, leading to destruction
of all underwater
life.
Water is an excellent solvent
and, as an accumulator of
heat, a significant climatic
factor as can be seen in the
case of the Golf Stream.
Two thirds of the human
body consist of the substance
water.
We could not live without
water. A human being can
survive for several weeks
without food, but only a few
days without water.

The
Blue
Planet
Almost three quarters of the
earth’s surface (71 percent) is
covered by water, the world’s
total water amounts to some
1.5 billion cubic kilometres.
Not one single drop of this
huge volume of water is lost,
no matter how or for what
purpose the water is used:
Above oceans and land the
surface water is evaporated
by the sun, this then is
changed into water vapour.
The water vapour rises and
condenses to form clouds,
which in their turn pass back
their moisture as rain, dew,
snow or hail, returning once
again to the evaporation
process from the oceans,
lakes and rivers – the neverending
water cycle.
However 97.2 percent of
total water supplies is salt
water and consequently is
not available as drinking
water, at least not directly.
Thus, this leaves 2.8 percent
freshwater, but the bulk of
this is frozen water to be
found in the polar ice caps
and glacier ice as well as
being confined to the atmosphere.
A mere 0.7 percent
of total water on the earth is
immediately available as a
drinking water resource.

With a mean average annual
precipitation of 790 millimetres
Germany is a region
with an abundance of water
(this is the equivalent of a
volume of 790 litres per
square metre). Taking into
account the loss of water due
to evaporation and flowing
to neighbouring countries
and allowing for water flowing
into Germany from the
latter, the water resources
available in our country is
182 billion cubic metres.
The Water Budget illustrates
how this volume is split up
between the consumer
groups. It is obvious that
public sector water supplies,
amounting to some 5.7
billion cubic metres annually,
represents only a small proportion.
At the same time it
is apparent from this Budget
that less than a quarter of
the total amount available is
actually used – therefore we
have no problems regarding
lack of water.
Of greater significance is the
threat to drinking water resources
from industry (waste
water from production processes),
agriculture (soil
penetration of fertilisers and
pesticides) and private households
(two million tons of
household cleaners and detergents
annually). The waterworks
are concerned about
having to invest even more
money in the future in order
to be able to supply drinking
water with the required
quality.
With this in mind Stadtwerke
Düsseldorf actively supports
the appeal made by the
Association of Waterworks in
the Rhine Catchment Area
(IAWR):
The quality of surface water
is intended to be sufficiently
high to permit only
natural methods for treatment
of drinking water.

Düsseldorf –
the Water Supply
The Stadtwerke Düsseldorf
waterworks supply over
600.000 people in Düsseldorf
and Mettmann with an
average of 150.000 cubic
metres of drinking water a
day – that is 150 million
litres. (As an illustration,
that is the equivalent of
750.000 bath tubs, each
holding 200 litres). The
water supplied can vary between
120.000 cubic metres
on a winter’s day and
200.000 cubic metres on a
hot day in summer.
Even then there are no
problems. Maximum capacity,
otherwise known as
”bottleneck capacity”, is in
the region of 252.000 cubic
metres per day. In addition
to this almost 120.000 cubic
metres are retained in four
reservoirs, where brisk stirring
and intermingling of
the water ensures consistent
quality.
Water supply is maintained
by three waterworks:
“Holthausen” waterworks in
the south of the city, where
the laboratory responsible for
quality maintenance and supervision
is located.
“Flehe” waterworks, in the
vicinity of the Heine-University,
which in 1870 was the
nucleus of the central supply
of water in Düsseldorf.
“Am Staad” waterworks to
the north of the trade fair
grounds, which is the control
centre for the Rhine leftbank
emergency waterworks
“Lörick”.
In order to ensure adequate
supplies of water the Düsseldorf
waterworks, for instance,
are linked up with
the Great Dhünn Valley Dam,
the ground water extraction
facility of the lignite mining
area and the waterworks of
other towns in the vicinity.

Water Supply in
Düsseldorf involves
three distinct stages:
Water Production
Water Processing
Water Distribution
Water Production
The wells of our waterworks
produce a natural water,
approximately a quarter of
which consists of ground
water and some three quarters
of Rhine water seepage;
these proportions can vary
somewhat, depending on the
water level of the Rhine.
The river water seeps off at
the bottom in the middle of
the Rhine river bed and runs
slowly in the direction of the
bank. The passage through
the bank and layers of sand

Rhine
water-bearing
gravel and sand strata
water-carrying bed
local water table
lowered ground
water table
well
pump
and gravel, up to 30 metres
thick, can take several weeks
until the water reaches the
well pumps. During this period
the water is purified
twice over: firstly the gravel
and sand function as a mechanical
filter, holding back
dirt and turbid substances.
Secondly micro-organisms,
minute forms of life, eliminate
a large number of substances.
This natural biological
process prevents the
slotted pipes
pipe to processing plant
ground water from
Rhine-Berg-District
layers of soil from being burdened
with harmful substances
and thereby depriving
them of their function – in
actual fact the bacteria live
off substances that the
drinking water can well do
without by destroying them.
Thus the water at the pump
well (known as “raw water”)
is of high quality, even at this
early stage.
The pumps in the well lines
extend down to a depth of
30 metres and cause the
subterranean water table to
drop. In this way there is an
uninterrupted flow of water
to the wells The water is
drawn in via pipes with slotshaped
openings and pumped
into the waterworks via
collector pipes.

Water Processing
Processing the raw water
is achieved by means of
the “Düsseldorf Process”,
a process which has been
developed by the Düsseldorf
waterworks .
First of all the water flows
through a contact tank and
ozone (O ), this is the highly-
3
active trivalent form of oxygen,
is added to it. Ozone
functions as a highly effective
disinfectant and transforms
organic and inorganic
substances into flaky precipitants,
which can be readily
filtered off. In particular
these are iron and manganese
compounds. Simultaneously,
odours and tastes,
which can affect the quality
of the drinking water are
removed.
The ozone treated water is
retained in an intermediate
tank for some 30 minutes
for a further reaction. Any
substances which have not
been previously treated are
then converted. The residual
ozone leaves the tank via a
catalytic converter and is
passed back to the air as
normal oxygen are now
converted.
The third step in the processing
chain is the filtration.
The water is pumped into
a steel tank filled with two
layers of carbon. As the water
seeps through the 1.5
metre deep upper layer the
flaky precipitation is removed
and organic substances
microbiologically eliminated.
When in due course the efficacy
of the filtration process
deteriorates the carbon is
washed. The sludge rinsed
out holds a high proportion
of carbon shavings and is
incinerated.

ozone gas
from ozone
unit
injector
motive water
catalyctic converter
for removal of
residual ozone
natural water inlet contact tank intermediate tank active carbon tank
The second layer, 2.5 metres
deep consists of active
carbon, a very fine and
extremely porous granulate.
Organic chlorine compounds,
odours and tastes
and other undesirable substances
are retained in the
capillary tubes. As soon as
50% of the active carbon is
affected by residues, the
layer is removed and replaced
by fresh carbon. The
carbon is cleansed by calcination
at a temperature of
700 to 800 °C in its own
reactivation unit.
The active carbon is removed
immediately and replaced by
fresh activated carbon, if the
waterworks report abnormal
or hazardous incidents of
pollution of Rhine water.
pump
chlorine
dioxide
phosphate/
silicate
upper
layer
lower
layer
carbon
removal
vent
drinking water
outlet to network
The fourth and last step
involves adding a phosphatesilicate
mixture to the water,
initially in small doses
(1 mg/l) in order to prevent
damage to the pipes from
corrosion.
Finally 0.06 mg/l chlorine
dioxide is added to prevent
the formation of bacteria in
the water. The water undergoes
a constant check for a
large number of substances
which it might contain, not
only before it enters the network,
but also after it is in
the system for the purposes
of complying with the regulations
of the Drinking
Water Act. In this way our
customers can expect excellent
drinking water round
the clock.

Extract from the Düsseldorf Drinking Water Analysis
2002 2003
Water temperature 13.1 °C 12.9 °C
pH value 7.2 mg/l 7.23 mg/l
Total hardness 14.1 °dH 15.7 °dH
Hardness range 3.0 3.0
Calcium 89.0 mg/l 92.0 mg/l
Magnesium 11.4 mg/l 23.0 mg/l
Sodium 37.0 mg/l 39.0 mg/l
Potassium 4.5 mg/l 4.3 mg/l
Sulphate 63.0 mg/l 62.0 mg/l
Chloride 71.0 mg/l 73.0 mg/l
Nitrate 15.4 mg/l 16.2 mg/l
Phosphate 1.1 mg/l 1.02 mg/l
Water
Distribution
A 1.800 kilometre pipe network
extends throughout
the water supply area. With
a diameter of one metre the
pipes leave the waterworks,
eventually finding their way
to the end consumer’s
home, reducing to some
15 - 20 millimetres in diameter.
The pipes undergo
regular checks, are cleaned
and, if necessary, replaced.
In this way damage can be
identified in time before it
leads to leakage and loss in
the network.
Furthermore the quality of
water in the pipes is under
constant supervision: every
day samples are taken at
80 different observation
stations and tested by our
laboratory. All of the test
readings are registered and
monitored by the Municipal
Health Office.
An in-depth analysis of the
drinking water can be
obtained under the
following telephone number
from the utilities at any
time of the day:
+49 (211) 821 821 or
www.swd-ag.de

International
Cooperation
The Rhine has undergone
radical change since the
fifties and these are still
of great significance as far
as production of drinking
water is concerned.
The waterworks have
merged into regional
confederations in order to
promote their own interests
and requirements.
In 1950 the Dutch set up
RIWA (Rijncommissie
Waterleidingsbedrijven), in
1957 the German waterworks,
extending to the
mouth of the Neckar, established
ARW (Association of
the Rhine-Waterworks) and
in 1968 the south German,
French and Swiss water
suppliers launched AWBR
(Association of the Lake
Constance-Rhine Waterworks).
In order to consolidate the
resources of the individual
confederations and to act in
unison whilst promoting
the interests of the water
industry at the European
Union, IAWR was founded
in 1970 in Düsseldorf
(Internationale Association
of Waterworks in the Rhine
Catchment Area). Currently
120 waterworks from seven
countries are members of
IAWR.

Protection for
valuable resources
Drinking water is exposed
to numerous hazards. It
should not be overlooked
that a constant strain on
resources, entailing even
only minute quantities, can
be a greater burden than a
temporary high concentration
of harmful substances
caused by an accident at a
chemical plant. Thus this a
is a challenge to each and
everyone of us. We have to
reconsider our attitudes
radically: Nowadays it is all
too convenient to strew
weed killers where in former
times the weeds were simply
pulled up from the garden.
People resort to any of
the countless home care
products available rather
than taking the trouble to
keep the home clean, just
using water, brush and floor
cloths. This should not
however obscure one’s view
regarding practical quality
requirements for production
of drinking water. If it is a
generally accepted fact that
these products can be used,
it is unreasonable to expect
the waterworks to function
as a technical helpdesk for
the purposes of remedying
harm caused to the
environment.
Much has been achieved to
protect the Rhine as our
major source of drinking
water. A number of waterworks
confederations set up
an early warning system as
early as 1960, which informs
all the participants of
any significant incidents in
a link-up from Basel to
Rotterdam. Furthermore a
fleet of so-named “bilge-oil
extraction vessels” has been
established. These vessels
collect the bilge oil, which
accumulates in the bilge of
a vessel and dispose of it
efficiently and free of
charge. Last, but not least,
these confederations carry
out research projects, involving
not inconsiderable expense
and academic support
in order to improve the
water quality – but, nevertheless,
what has been
achieved to date can only
be preserved and enhanced
if everybody makes a contribution.

Imprint
Publishers
Stadtwerke Düsseldorf AG
Abteilung Öffentlichkeitsarbeit
Höherweg 100
40233 Düsseldorf
Phone: +49 (211) 821 821
Internet: http//www.swd-ag.de
E-Mail: pbeardsley@swd-ag.de
Text
Michael Pützhofen,
Stadtwerke Düsseldorf AG
Concept, Layout and Illustration
Palmer Jurk Design, Meerbusch
Picture Credits
– SWD-Archiv
– Stockbyte
– Goodshoot
– Adobe
– Photo of the earth with
kind permission of NASA B-102/99/12.02