Switzerland's drinking water is of excellent quality, but there is no
room for complacency. The challenges are growing: undesirable contaminants
are found in rivers, lakes and groundwater. Climate change is also warming
waterbodies, with implications for water quality, and in developing
countries more and more people are reliant on groundwater containing
natural contaminants. In Switzerland water utilities are ageing and need
to be renewed. In partnership with the water sector, the aquatic research
institute Eawag is identifying ways of ensuring that high-quality drinking
water supplies remain available in the future.
Various models predict that rising atmospheric concentrations of
greenhouse gases will lead not only to increases in air temperatures but
also to warming of waterbodies. This prediction has been confirmed by
observations: since 1945, for example, water at a depth of 5 m in Lake
Zurich has warmed by around 1°C in the winter and by almost 2°C in the
summer. The same trend is apparent in rivers. For the first time,
researchers have now also compiled long-term time series for groundwater
temperatures. Taking the example of groundwater at Rheinau (Canton
Zurich), they have shown that the temperature of the water in the winter
has risen by about 3°C since the 1950s. At the same time, the oxygen
content has constantly declined. During the 2003 summer heatwave, water
completely devoid of oxygen was pumped from certain wells in the Thur and
Glatt valleys. In the absence of oxygen, however, iron and manganese are
dissolved below the surface. These substances then have to be removed
before the water can be supplied to users. In lakes, higher temperatures
can also have adverse effects on water quality: the spread of
cyanobacteria (blue-green algae) is promoted. This may be problematic
since these growths include species that produce toxins or taste and odour
compounds. In addition, microorganisms generally grow more rapidly in
warmer water. In future, more elaborate treatment methods could be
required in places where drinking water has previously been supplied
untreated or after only simple processing.
The safety of water supplies depends crucially on continuous
monitoring. However, traditional methods for microbiological analysis of
drinking water involve the growth of visible colonies of bacteria on
nutrient plates. The plating method is time-consuming and underestimates
the number of microorganisms contained in water samples. Eawag has now
developed an analytical method based on flow cytometry. This process, in
which cells pass through a laser beam, has mainly been used to date in
medicine, e.g. for blood cell counts. At Eawag, it was adapted so as to
permit reliable enumeration of bacterial cells. Rather than having to wait
for 18–24 hours, results are now available within 15 minutes. In close
cooperation with Zurich Waterworks (WVZ), the researchers demonstrated
that the results stand up well in comparison with conventional methods. In
fact, they even provide a considerably more realistic picture, since
special labelling means that the method also detects microorganisms which
do not reproduce on nutrient media and have therefore been incorrectly
considered to be inactive or dead. What makes the new method especially
attractive – particularly for monitoring the microbiological safety of
drinking water in developing countries – is the fact that, using specific
antibodies, it is possible to screen samples for pathogens such as
intestinal parasites and legionella or cholera bacteria. This would
facilitate a rapid response in the event of contamination.
In Switzerland, 43% of drinking water is sourced from springs, 40% from
groundwater and 17% from lakes. Treatment is required mainly for lake and
spring water. Together with partners from the engineering sector and WVZ,
Eawag researchers have sought to identify the methods and combinations of
processes best suited for meeting future challenges. Substantial
investments are required to renovate water utilities, and new facilities
are expected to have a lifetime of 30 or even 50 years. At a pilot plant
in the WVZ Lengg lake water facility, it was shown that space-intensive
sand filters could be replaced by ultrafiltration membranes with a pore
size of 10 nm (1 nanometre = a millionth of a millimetre). Apart from the
saving in space, membrane filters offer the additional advantage of
representing an absolute barrier to microorganisms. The combination of
ultrafiltration with ozonation and activated carbon filtration, both of
which are already used today, adds up to an extremely effective process
chain for water treatment. It guarantees microbiologically safe drinking
water, which can be supplied without chlorination – a process frowned upon
by consumers. Any trace contaminants are efficiently removed.
Taking precautions and identifying risks
Experts are agreed that the most important type of protection for
drinking water is provided not by technical treatment processes, but by
careful management of water resources. Pollution needs to be prevented
wherever possible. Since many groundwater wells in Switzerland are located
close to a river, Eawag researchers have investigated what happens when
riverbeds are widened in restoration projects. Using a specially developed
method, it is possible to predict how likely it is that the water at a
nearby pumping station is no longer "genuine" groundwater, but river water
which has not been sufficiently purified as a result of a short residence
time in the subsurface. Depending on the risks involved, this may mean
that it is necessary to abandon or impose restrictions on a given river
widening project.
Risk identification of a quite different kind is the subject of the
"Water Resource Quality" research project (WRQ). Worldwide, millions of
people rely on groundwater contaminated with health-threatening arsenic or
fluoride of natural (geogenic) origin. With the aid of geological data and
computer modelling, Eawag researchers have produced global maps indicating
areas with a high risk for the occurrence of arsenic- or
fluoride-contaminated groundwater. This mapping procedure, which has also
already been successfully applied on the regional scale, is a valuable
instrument for authorities, aid organizations and water suppliers. The WRQ
project also involves efforts to develop and test simple, low-cost
treatment methods particularly suitable for use in developing countries.
SOURCE: Eawag - Swiss Federal Institute Of Aquatic Science And
Technology