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It is very important that water used for any purpose is of a quality
suitable for that purpose. If the quality is superior by a small amount,
then no harm can result. Pure water is unsuitable for many purposes,
including drinking and irrigation. It is therefore important that the
impurities present are compatible with the use to which the water is put.
Ordinary water as distributed by municipal systems should be lightly
mineralised and, preferably, with a small amount of lime and carbonates
(soft). If the water is too hard, washing with soap will require a heavier
consumption due to the presence of scum formed by the chemical reaction
between the soap and the lime and carbonates. It is therefore in the
interest of economy to ensure that municipal water is not too hard. This may
be done by diluting the hard water from limestone sources with the very soft
water produced by reverse osmosis desalination. Municipal water has to be
exempt from harmful bacteria and other microorganisms and this is usually
done by one of two methods. Throughout the world, the most usual one is
chlorination which is very effective but requires careful dosing. If the
quantity of chlorine is insufficient, there is a risk that bacterial
contamination may proliferate, especially if the water source may be
contaminated from septic tank seepage. Too much chlorine is wasteful and
gives the water an unpleasant odour. The other method is by ultraviolet
radiation and is achieved by passing the water through quartz pipes
surrounded by intense ultraviolet lamps. These lamps ionise the dissolved
oxygen in the water to form ozone which is a powerful sterilant. Some of the
microorganisms may also be directly attacked by the ultraviolet light. This
method is, by far, the most reliable and easy way of ensuring the sterility
of potable water for small installations, because there is no handling of
obnoxious chemicals and dosing is not a problem.
One impurity that is common in some areas of Cyprus and may also be
present in desalinated water is boron. The quantities present are usually so
small that it has no effect for any use, although the concentration does
have to be kept within specifications for potable water. Citrus trees need
boron at a concentration of 0.1-0.5 ppm for healthy growth and production.
In alkaline soils, there may be boron present but it may be sequestered from
the plant. However, citrus is very intolerant of excessive quantities of
boron and a concentration of 20 ppm in irrigation water may be sufficient to
kill otherwise healthy trees.
Wet Analysis
Wet chemical analysis is used extensively for determining water quality.
It can measure the exact quantities of any dissolved solids and also such
components as oils and organic solvents. In addition, modern laboratory
equipment can automate many of the procedures by means of infra-red
spectrography, ionic chromatography and liquid chromatography.
Electrical Conductivity
Electrical conductivity can easily be measured with cheap, portable
equipment. The conductivity of the purest water possible is 0.056
microsiemens-centimetre, but this value is obtainable only under laboratory
conditions. In practice, values in the range of 100 to 10,000
microsiemens-centimetre are common for potable water. This type of
measurement gives a certain measure of all dissolved ionic (metallic) salts,
without indicating which ones are present.
Total Dissolved Solids
Total dissolved solids are a measure of the weight of the residues, in
milligrams, after evaporating one litre of carefully filtered water. The
conditions under which this test is conducted are carefully laid down in
international specifications.
Undissolved Solids
Undissolved solids are the aggregate of silt and microorganisms which are
retained in a mechanical filter with a pore size of given dimensions,
according to the required specifications. As a general rule, the pore size
will be within the range of 0.5 to 5 micrometres.
Organic Matter
There are several types of organic matter which may be found in water and
their determination depends on the nature of the matter. Basically, the
organic matter can be divided into living and chemical natures. The living
matter or microorganisms comprise a wide variety of life forms. The chemical
matter may be either natural or man-made pollution. As an example of natural
pollution, the presence of decayed vegetable matter may be cited as one
example. By far the more serious type of chemical pollution is that produced
by the activities of Man. The worst examples are the addition of
non-biodegradable or poorly-biodegradable products into water, e.g.,
lubricating oil, organic solvents and suchlike. One litre of oil or solvent
may render hundreds of tonnes of water unsuitable for human consumption and
care must be taken always never to allow such pollutants to enter the soil
or water courses. Less serious, but nevertheless not negligible, sources of
pollution include biodegradable compounds such as soaps and detergents and
inorganic additives to them, such as phosphates.
The identification of non-living organic pollutants can be done by
chemical analysis. There are two useful methods of determining whether water
polluted from organic sources is likely to present problems in the long
term. The chemical oxygen demand can be determined in laboratories as a
measure of the oxygen required to convert organic matter into water and
carbon dioxide under given conditions. The biological oxygen demand is a
similar measure of the oxygen required to sustain bacteria which will
naturally break down some organic pollutants. This bacterial action is
similar to that which takes place in septic tanks and sewage treatment
plants.
Some organic products are very toxic, whether they are biodegradable or
not. One example is the use of certain types of specialised non-ionic
detergents called octyl- and nonyl-oxyphenoxylates. These biodegrade readily
but incompletely, one of their decomposition products being particularly
toxic to aquatic life and down the food chain. Such detergents are still
found in some specialised industrial products.
The microorganisms that can be found in water fall into a wide number of
categories. The major ones include:
- Viruses
- Bacteria
- Amoebae
- Algae and their spores
- Microplankton of vegetable and animal origin
- Etc
Of these, the viruses and bacteria may be very dangerous to human health
in drinking water, being direct disease vectors, and must be killed by
chlorination or ultraviolet radiation. They are responsible for such
diseases as cholera, typhoid, paratyphoid and other one. Amoebae can be
responsible for some very severe forms of dysentery and microplankton can
cause a number of other serious diseases, often through parasites having
undergone development in other vectors, such as liver fluke, bilharzia and
elephantiasis.
The detection of larger microorganisms is done through microscopic
examination. Smaller microorganisms can be detected only after culture in a
suitable medium, which may take considerable time. Electron microscopy may
also be a useful tool for identifying species.
The major source of dangerous microorganism pollution is through the
infiltration of faecal matter into the water. The large number of septic
tanks in Cyprus, some of very old or doubtful construction, makes this a
real risk for water which is pumped from sources close to the surface. Such
water should never be used as potable water except after controlled
treatment. Another source of similar pollution is from leakages in sewage
systems. Similarly, it must never be assumed that any surface water is free
from harmful microorganisms.
Hardness
The hardness of water depends on the presence of calcium or magnesium
hydroxides and carbonates. The effect of hard water is to form a scum when
soap is added. This has a double effect in that it requires more soap to
generate a lather hence increasing the pollution in the waste water and that
it requires more water to eliminate the scum and extra soap in what has been
washed. There are several ways of expressing the hardness of water, some of
them being used in a specific country: these ways are not necessarily
convertible as the method of measurement may be different. One of the
commonest methods of measurement is to add enough of a standard soap
solution to form a stable lather, the hardness being related to the quantity
of soap used.
Whereas hard water is not desirable, neither is very soft water which is
unpalatable for drinking. In many areas where the water is naturally soft,
lime is often added to increase the hardness, such as in Scotland. Much
purified water is very soft.
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