Water Quality

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.

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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