Water - Sources and Contamination | Evaluation of Water or Water Qualities.

(Part 5, Environmental Hygiene, VPE) 

Topic: Water - sources, contamination and their prevention. Water qualities or Evaluation of Water- physical, chemical, biological and bacteriological.

Water - Sources, Contamination and Evaluation

Water - Sources and Contamination | Evaluation of Water or Water Qualities.

Water Sources

Water is indispensible to support life and to help in the productive processes of animals. Water is also needed for many other operations in the farm to maintain the cleanliness of animals and their habitations and to process many of the animal products like milk, butter, cheese and meat. Water is also needed for cleaning various utensils used in the handling of animal products. This aspect has a direct bearing on public health, hence the water supplies should confirm standards. Lack of knowledge on the quality of water and its source will bring down the efficiency of farm management leading to general breakdown in the health and production of animals. 

The natural sources of water 

  • Rain water 
  • Surface water 
  • Brooks 
  • Streams 
  • Rivers 
  • Lakes 

Underground Water 

  • Subsoil water 
  • Deep ground water 
  • Springs

Rain Water :

  • This is precipitation of water which is obtained as the condensation of moisture in the form of rains, snow and dew. 
  • The amount of rain water depends upon the rainfall, and the distribution of rain over a period in particular region. 
  • The two monsoons , the south west and north east monsoons bring about 80 per cent of total rainfall. 
  • The rain water must be collected in suitable natural basins or artificial reservoir and stored as a source for use in the farm. 
  • Rain water at its origin is the least polluted water with minimum impurities but as it descends down it gathers various impurities /pollutants depending upon the activities of the region. 
  • Rain water collected under the rural conditions is less polluted than that collected under the urban conditions. 
  • Rain water collected from highly industrialized places are heavily contaminated with toxic matter or harmful matters. 
  • In general rain water is comparatively pure and is soft in nature with less of dissolved impurities. 
  • It is insipid in taste and some times it will acidic in reaction, having plumbo solvent characters with corrosive properties.

Surface Water :

  • Surface water is the natural collection of rain water, that has fallen on the earth, washed the surface and collected in the form of rivers and lakes. These are most common and economical sources under natural farming conditions, where there is a good rainfall. In the absence of good rainfall, most of these sources will be dried up. 
  • Surface sources in general provide a poor quality water sometimes the water may be dangerously polluted by manure and land washings. 
  • The quality of such water changes due to the influence of rain and sun. The lake water is highly impure even when it is freshly collected. The river water is least populated as its origin but as it travels it gathers impurities in the form of land washings and household sewage and various industrial effluents discharged into the river. 
  • Polluted river water when it travels more distance it undergoes certain amount of self purification, due to natural sedimentation, absorption of oxygen and oxidation, percolation into the beds and reappear in the form of springs. 
  • The exposure of vast sheet of water to the ultra -violet rays of the sun is also responsible for self purifications. 
  • The mineral content of the river water depends upon geological strata of the earth through which the water flows. 
  • The chemical character of river water is subjects of wide variation according to the nature of the gathering grounds and also to the different geological formations through which the river bed passes. 
  • Dissolved solids taken up in one are may be deposited in another area. The bacterial quality of water depends upon the amount of river pollution taking place and the chances given for self purification of water. 
  • Hygienic measures should be taken for the protection of surface water sources to prevent pollution and contaminations by preventing the mixing up of industrial wastes wash water from livestock farm and dwelling places.
  • Public health acts as well as river pollution prevention act should be enforced undue pollution with sewage, industrial effluents should be checked. 
  • Gathering grounds or catchment are such as lakes should be protected by high raised wall/fencing, preventing unauthorized entry of livestock and human beings and should be maintained as per the public health regulations.

Underground Water :

The water is held beneath the soil and it has to be tapped in the form of wells or springs. 

Two categories of Underground Water 

  1. Sub soil water 
  2. Deep ground water 

Sub Soil water 

  • This water is held above the first impermeable layer and it rises and falls according to the season and rainfall of the locality. 
  • The sub soil water is liable to gross contamination form organic vegetable wastes and livestock excretory pollutants. 
  • The fitness of the sub soil water as a source for the livestock should be regarded with suspicion and such water has to be submitted to bacteriological examination before put to use. 

Deep ground water 

  • This water lies below at least one impermeable stratum. As it has percolated to a greater depth it is usually free form significant bacterial pollution. 
  • Water is protected form surface pollution by the presence of impermeable strata. 
  • Even this ground water sources may occasionally be grossly polluted and contaminated due to certain natural faults such as cracks, and fissures in the course of rock formation. 
  • Mineral contents of ground water is generally very high.

Springs :

These are natural outlets of underground water and they supply the water at the surface of the earth in the form in different springs 

Land spring or dip spring (intermittent) 

  • Whenever there is a dip in the land exposing the impermeable stratum to the surface the water comes out in the farm of land spring. The water is doubtful purity and its supply is seasonal.

Fissure spring 

  • This spring occurs due to the presence of deep fissure or crack in the rock upto the water bearing stratum. 

Junction spring 

  • This spring results form the geological fault occurring due to two different strata coming together and forming a junction. 
  • Deep ground water comes out in the form of spring at the junction of the strata. 
  • The last two springs are permanent springs supplying good quality water with lesser seasonal fluctuations. These natural springs can be developed into good water sources. 
  • An artificial basin should be constructed for collection of such water. 
  • Fence should be provided all around to prevent unauthorized entry of human beings and animals. 
  • The quality of water is similar to that of the deep underground water

Classification of Water : 

Classification of water according to their palatability and wholesomeness is as follows

Types of Water.

Water Contamination 

  • Sewage from un-sewered area 
  • Faulty municipal sewerage system 
  • Storm water run off 
  • Industrial effluents 
  • Agricultural - Leachates from household and industrial solid wastes and infiltration of fertilizers and pesticides from agricultural areas. 
  • The house hold effluents are discharged into open sewers which often infiltrate into the surface water sources. Deficiencies in the sewerage systems such as overflow of untreated sewage from deficient pumping stations and clogged sewerage pipelines. Leakages from badly maintained sewerage pipelines are major pollutant sources and clogging of sewers often occur due to uncontrolled dumping of solid wastes. 
  • In many places where sewers are connected to the storm drains. This results in contamination water sources. In general many drains are silted up and choked with vegetation. Thus large areas particularly the low lying areas are flooded during rainy seasons and water stagnates for several weeks after the rains. This may result in contamination of potential ground waters. Furthermore the washout of accumulated waste and debris from the storm drains during the rainy season results in pollution of sediments in the surface waters near the outfalls. 
  • Non treated or poorly treated waste water from the textile plants , tanneries, distilleries leachates from hazardous waste. eg fertilizer, petrochemical and caustic soda plants also contaminate the water 
  • Agriculture: Due to uncontrolled use that significant amount of fertilizers and pesticides infiltrate to the surface water.

Main Source Area  & Possible Sources. 

Sewerage Systems 

  • Lack of systems in un sewered areas, slum areas. 
  • Leakages and over flow from the sewerage pipelines. 
  • Overflow fom deficient pumping sytems. 
  • Inadequate sewerage treatment facilities inclusive pipelines and pumping station for treated waste water. 

Storm Water 

  • Over flow from drainage with wash out of accumulated

Industrial effuents 

  • Inadequately treated industrial effluents. 
  • Leakage and spillages of chemicals. 
  • Irrigation water from distilleries and textile plants. 

Municipal solid waste 

  • Leachates from inadequate collection facilities, uncontrolled dumping sites and unprotected land fills. 
  • Uncontrolled dumping into surface waters and sewers. 
  • Industrial solid wastes inclusive of hazardous wastes. 
  • Leachates from onsite storage, uncontrolled dumping sites and unprotected landfills.

Energy plants 

  • Leachates from coal, cinders and fly ash. 


  • Infiltration of fertilizers and pesticides 

Sea water 

  • Over exploitation of ground water, tidles

Evaluation of Water or Water Qualities

Physical, Chemical, Biological and  Bacteriological Evaluation of Water are discussed here.

Physical Evaluation of Water :

Water sample is evaluated physically for colour, turbidity, odour, taste and electrical conductivity 

  • Colour and Turbidity 
  • Odour and Taste 
  • Electrical Conductivity

Colour and Turbidity

  • Natural waters rarely show colours other than yellow or reddish brown, which usually indicate the presence of peat acids or , in the case of turbid water, suspended particles clay or iron oxides: occasionally algal growth is responsible for the appearance of a green or red colour. 
  • Few waters which can be considered satisfactory contain appreciable quantities of suspended organic matter. 
  • Its presence in any quantity encourages the growth of micro-organisms, renders the water difficult to filter, and frequently makes sterilization difficult. Suspended mineral matter, on the other hand , is less objectionable. 
  • Its presence tends to be seasonal, occurring usually after periods of heavy rain, although when in the form of hydrated oxide of iron it appears as a permanent turbidity in ferruginous waters.

 Odour and Taste

  • Odour and taste can only give an indication of sewage contamination if it is excessive , but they are useful in detecting other unusual types of contamination which are difficult to detect chemically. 
  • For example, the accidental contamination with small quantities of paraffin oil or similar substances sometimes occurs; chemical methods may not be sufficiently sensitive to detect traces of these compounds, and in such cases taste and smell may be the only guides to the presence of these contaminants. 
  • Peaty water nearly always has a slight adour. Certain waters contain sulphuretted hydrogen. 
  • Decomposing aquatic fauna and flora in service mains are not infrequently the cause of “smelly” water.
  • Rain water has a flat insipid taste. Soft waters taste “soft”, Ferruginous waters taste of ink. Waters containing much sodium chloride have a brackish taste. 
  • The water from newly laid mains may have a tarry flavour. 
  • Water treated with bleaching powder tastes of chlorine if the available chlorine in the water exceeds three of four parts per million. 
  • Hard waters, and also those containing nitrates and carbonic acid, are more palatable than soft waters of those free from gas in solution.

Electrical Conductivity

  • Chemically pure water is a non-conductor of electricity, but the solution in it of ionisable salts renders it conducting, the case with which an electric current is transmitted being directly proportional to the concentration of ionisable salts in solution. This fact is made use of in the examination of natural waters, the electrical conductivity of the water being an indirect measure of the amount of dissolved substance present it. 
  • It should be noted that, by itself , the electrical conductivity gives no indication of the nature of the substances in solution. 
  • Values of electrical conductivity for natural waters vary from about 100 gemmhos for soft waters derived from the older crystalline rocks to about 2,000 gemmhos for very hard waters derived from the newer and softer rocks; sea water has a conductivity of about 50,000 gemmhos. 
  • In the absence of sodium salts, the electrical conductivity is proportional to the hardness, one degree of hardness raising the electrical conductivity by about 20 units. Thus such a water with a conductivity of 500 units , would possess a hardness of approximately 250. 
  • The determination of electrical conductivity finds its greatest use in indicating changes in the amount of dissolved solids present in a water where the composition of the dissolved solids fraction is known and is fairly constant. 

Chemical Evaluation of Water :

The complete chemical examination of water in respect of its suitability or otherwise for drinking and for ordinary domestic uses normally includes determination of total solids, pH, hardness , free and albumoinoid ammonia, nitrate , nitrite, chlorides, and action on metals. 

It may also be necessary to examine waters for unusual constituents such as lead, zinc, arsenic, copper, iron, aluminium, magnesium, fluorides and cyanides, whose presence may be suspected from a consideration of the source of supply or from a history of toxic symptoms arising in man or animals drinking the water. 

Whilist the chemical examination and the interpretation of the results falls strictly within the province of the experienced analyst, some knowledge of the procedures involved will greatly aid the veterinary surgeon in appreciating the significance of the analytical findings. 

  • Total Solids 
  • pH value 
  • Hardness 
  • Chlorides 
  • The Nitrogen Constituents 
  • Reducing Powder or "Oxygen Absorbed"

Total Solids

  • The method of determination employed is briefly as follows:- The residue left after evaporating a measured volume of water is weighted and the result calculated to parts per 100,000 of water. 
  • The estimation is usually carried out on filtered water if appreciable quantities of suspended solids are present, so that suspended solids are reported separately from dissolved solids. 
  • The residue consists of all the non-volatile substances which were present in solution in the original water. 
  • The organic content of the residue can be assessed from the appearance of the residue after gentle ignition, considerable charring indicating a high content of organic matter. 
  • Satisfactory waters rarely contain more than 80 parts per 100,000 of dissolved solids, and for most purposes should contain much less; they rarely contain more than a mere trace of organic matter

pH Value

  • The pH of natural waters is of importance chiefly from the point of view of possible corrosion of metals. 
  • Waters with low pH values, especially if the acidity is due to dissolved carbondioxide or to humic acids are potentially plumbo-solvent; they corrode most metals to some degree. 
  • Akaline waters , particularly if the alkalinity is due to dissolved sodium carbonate are corrosive of zinc. 
  • It should be pointed out that waters which are neutral in reaction are not necessarily non-corrosive, e.g. neutral solutions of chloride and nitrates will corrode most metals. 
  • The pH value of a sample of water should, therefore, be considered along with other determinations, particula


  • The hardness of water refers to its soap-destroying power and is due to the presence of calcium and magnesium salts in solution. 
  • It is usual to distinguish between waters that are “temporary” hard and those that are “permanently” hard . 
  • Temporary hardness is due to the presence of the bicarbonates of calcium and magnesium in solution, permanent hardness is due to the chloride, sulphates and, to a lesser extent, the nitrates of calcium and magnesium. 
  • Hardness, whether temporary or permanent, is expressed as parts of calcium carbonate per 100,000 parts of water; “degrees „‟of hardness are numerically equal to parts of calcium carbonate per 100,000 parts of water. 
  • A total hardness of more than 30 is sufficient to render a water unsuitable for most purposes , although if required for drinking only a considerably higher hardness might be tolerated. 
  • Waters with hardness less than 5 are very soft, and such hardness values should be considered along with pH value for possible plumbo-solvent action.


  • Chlorides are rarely absent from natural waters, being present chiefly as sodium chloride, with occasionally magnesium, potassium and calcium chlorides. 
  • The chloride content of waters derived from rocks near the sea is invariably high; waters from deep wells may contain sufficient to impart a brackish taste. 
  • The presence of chloride considered alone is therefore of little significance as regards hygienic quality, but as sewage contains appreciable quantities of it, if the chloride is present together with free ammonia, nitrite or appreciable quantities of nitrate, this finding may support an indication of sewage pollution. 
  • Uncontaminated surface waters (except near the sea ) rarely contain more than 2 parts of chloride per 100,000; well waters may contain considerably greater quantities.

The Nitrogenous Constituents 

  • Uncontaminated water supplies are rarely completely free from nitrogenous constituents, and in such waters nitrogen may be present in the form of humic acids or nitrates. 
  • Waters contaminated with sewage or other decaying organic matter may contain, in addition to these, ammonium salts or easily decomposable amides , and nitrites. 
  • As ammonium salts and nitrites are quickly oxidised in natural waters to nitrate, their presence is taken as a strong indication of recent contamination with sewage. 
  • Quantitatively the ammonium salts and easily decomposable amides are estimated by distilling a sample of the water made alkaline with sodium carbonate; the amount of ammonia distilling off is estimated calculated to part per 100,000 and reported as “Free Ammonia.” 
  • Humic acids and the more complex nitrogenous compounds such as protein do not liberate ammonia on boiling with sodium carbonate, but do so when distilled with an alkaline solution of potassium permanganate. This ammonia is estimated calculated to parts per 100,000 and reported as “Albuminoid Ammonia.” 
  • Satisfactory waters rarely contain any free ammonia at all, and the presence of more than 0.005 parts per 100,000 must be regarded as significant of pollution. 
  • If the amount of free ammonia present is greater than the amount of albuminoid ammonia then sewage contamination is certain. Many satisfactory waters, e.g. peaty waters, contain appreciable quantities of albuminoid ammonia but such waters yield their albuminoid ammonia slowly, and they contain only traces of free ammonia. 
  • In waters other than moorland waters, the albuminoid ammonia may be significant of sewage pollution if it is a present in concentrations greater than 0.01 parts per 100,000. 
  • The presence of nitrate is of no significance in the absence of other nitrogenous constituents. If, on the other hand, free ammonia is present then the presence of nitrate is an added indication of pollution.

 Reducing Power or "Oxygen Absorbed" 

  • The pollution of natural waters is invariably accompanied by an increase in the amount of organic matter present in solution. This dissolved organic matter is easily oxidised and the amount of available oxygen absorbed by the water from a oxidising solution gives a measure of it. 
  • The ability of water to reduce a dilute solution of acid potassium permanganate referred to as the Reducing Powder or Oxygen Absorbed figure, and is reported as parts of available oxygen absorbed per 1000,00 parts of water. 
  • Many natural waters contain dissolved organic watter that is innocuous . Moorland waters, for example, contain peat acids, and if the reducing powder of such waters is not in excess of about 0.1 parts per 100,000, they may be regarded as satisfactory. 
  • In the case of other waters the reducing power should not normally be in excess of 0.05 parts per 100,000. 
  • In all cases the reducing power should be considered in the light of the other estimations, e.g. free ammonia and chloride, that indicate possible contamination.

Biological Evaluation of Water :

  • All natural waters, excepting possibly some of the deepset underground waters, are inhabited by a diverse plant and animal life, the chief phyla of the former being Algae, Fungi and Bacteria, whilst the animal kingdom is represented by Protozoa, Sponges, Rotifers, Molluscs, various free-living “worms”, Insects, Fishes and Amphibia. 
  • The kinds of plants and animals found in any particular water depend largely on the character of the water and on the source from which it is drawn, and, as far as contaminant intestinal bacterial of human or animal origin are concerned, on the degree to which the water has been exposed to sewage and/or manurial pollution. 
  • In general , the flora and fauna of surface waters are more abundant and more diverse than those of underground waters, whilst those of the deepest subterranean waters are relatively poorer than the life of sub-soil waters. 
  • A few minute Crustacae feeding on bacteria and fungi are able to live in deep wells and in the subterranean waters on which they draw, but if the wells be of great depth or are poorly aerated the water will usually be devoid of living things. 
  • Few, if any, of the forms of life, apart from contaminant bacteria of intestinal origin, which may be found in natural waters would appear to be toxic or harmful to man or animals drinking the water. 
  • In the following paragraphs, some account is given of the more important forms of plant and animal life which are to be found in water supplies, and which may give rise to problems during the purification, storage, and distribution of the water.


  • The algae constitute the most ubiquitous form of plant life existing in freshwater; the majority are microscopic in size but some are visible to the naked eye, eg., the bright green thread-like algae often seen in ponds and streams. 
  • From the point of view of water supply, three groups of algae are of great importance, namely the Isokcnatae or Green Algae, the Myxophyceae or Blue-Green Algae, and the Diatoms. 
  • These and other groups of algae, which may only flourish moderately in the running water of rivers and streams, generally increase markedly in the comparatively still waters of lakes and storage reservoirs. This increase in useful in some ways. 
  • The aeration of the water by the algae helps to purify it and, as will be mentioned later, they play a vital role in the purification of water supplies by filtration processes but, if their growth becomes excessive, they may interfere with filtration.
  • Such excessive increases in the algal population of open storage reservoirs can be controlled by the application to the water of a chemical algicide, such as copper sulphate which is used at the rate of 1kg to 4.5kg. CuSo4 per 45,46,000 litres of water. Care must be taken to ensure the even distribution of the CuSO4 throughout the reservoir. 
  • The usual method of application is to tow a bag of the along carefully planned lines in the reservoir . 
  • It is better policy to use Cuso4 as a preventive against excessive algal multiplication in a reservoir than as a curative, in which case the dead algae undergoing decomposition may render the water unfit to use for time. 
  • Objectionable taste due to algal growths may be removed by dosing the water the with powdered activated carbon at the rate of 1 to 5 parts per million. The covering over of small reservoirs will effectively reduce algal growth therein. 
  • A great bulk of algae passing on from storage reservoirs to the filter beds during periods of algal abundance introduces mechanical difficulties in the filtration of the water, and unless the filtration plant is frequently cleaned the filter beds will become choked. 
  • The use of algicides in the filter beds is not practicable, as the purification of vary large quantities of dead algae may be even more objectionable than the presence of the living plants in the water. 
  • If it is necessary to remove offensive tastes after filtration about 0.5 part per million of potassium permanganate may be used.

Soil Bacteria

  • Ground-water lying near the surface will usually contain free-living bacteria derived from the upper few inches of the soil complex. 
  • These bacteria include aerobic forms which break down organic material into its simple component elements of carbon, nitrogen and hydrogen. 
  • This resolution process is further carried on by two groups of nitrogen-oxidising organisms, which convert ammoniacal nitrogen to acid radicles that in combination with existing soil bases form nitrites and nitrates. The first of these bacterial groups ( Nitrosomonas) converts ammonia to nitrites, whilst the second ( Nitrobacter) completes the oxidation process by converting the nitrites to nitrates, which constitute the completely oxidised state of N2. 
  • The bacteria which initiate the breakdown of organic material, as well as those involved in the oxidation of nitrogen, require for their efficient functioning the provision of adequate moisture, oxygen, suitable bases and an environmental temperature of over 50c. Unless this requirements are satisfied, the disintegration of organic matter cannot proceed to completion and the end products represented by the humic acids now formed cause “souring” of the soil. 
  • Water draining from a soil in which these condition pertain will be acid in character, as for example, the acid waters draining from water-logged peat accumulations, in which the incomplete breakdown of the excessive amounts of vegetable organic matter is due to the absence of oxygen and of suitable bases. 
  • The plant remains are finally converted to true peat by anaerobic bacteria. Sandy soils, which are always characteristically low in mineral matter, may also under certain conditions accumulate organic matter, because in the absence of soil bases (lime) the decomposition of plant debris cannot proceed, and layers of peat may be formed. 
  • Similarly, even on heavy land plant debris may tend to accumulate, e.g., many old grasslands have matted turves many inches thick which show little or no signs of decomposition if ploughed in unless lime is used to correct the soil acidity .
  • Another example of failure of this biological scavenging process sometimes occurs in connection with land treatment of sewage-tank liquor, where as a result of excessive application of the sewage liquor the alkaline bases in the soil become exhausted, and consequently the conversion of the acids formed by the nitrifying bacteria to nitrates and nitrites does not occur and they accumulate in the soil, rendering it “sewage-sick”. 
  • Such soil may have its purifying properties restored by the addition of 1 to 2 tons of lime per acre, combined with a period of rest from further sewage application.

Iron Bacteria

  • Certain of the Bacteria have the power of abstracting iron from the water in which they live and of depositing it in the form of ferric hydroxide in the mucilagenous sheath with which they are invested. 
  • The “ochre-beds” sometimes seen on boggy moorland streams are produced by the deposition of the iron impregnated sheaths of these bacteria, which sink to the bottom of the stream when the bacteria die. 
  • The presence of iron in their surrounding medium is not essential to the life of the Iron Bacteria, for they can flourish in its absence. 
  • The iron seems to be assimilated by the bacteria probably in the form of ferrous bicarbonate, along with nutrient materials, is oxidised to the insoluble hydrated ferric oxide, and is then deposited in this form in the filament sheaths of the bacteria. 
  • Crenothrix is perhaps the best known of the Iron Bacteria, though possibly it is not the most widespread. 
  • As normally found, it consists of minute filaments attached by one end to some solid object. 
  • Each filament consists of a single row of cells, the whole being invested by mucilagenous sheath. 
  • Rapid multiplication of Crenothrix in supply reservoirs has occasionally produced spectacular effects in the water drawn from the service main. The water was unusable for domestic supply owing to its bad taste and smell. 
  • The effect in water supply systems due to Gallionella, another of the Iron Bacteria, is less striking than those of Crenothrix, but this organism in probably far more widespread. 
  • Gallionella forms a slimy coating on the inner surface of iron supply pipes, from which streamers extend into the water; this coating may become so thick that it considerably reduces the capacity of the pipes, Gallionella also plays a part in the formation of the hard rusty nodules and incrustations that are commonly seen in water-pipes in some areas. 
  • The exact role of the bacteria in the production of these is uncertain, but it is thought that in some way they accelerate the deposition of rust, probably through their oxidation processes. 
  • Chlorination of the water is one of the remedies that have been found satisfactory in the control of Iron Bacteria and the troubles arising there from in public supply systems.


  • Since all free-living fungi are saprophytic, i.e. derive their nourishment from decomposing organic material, the occurrence of fungi growing in water is evidence of the presence in the water in question of decomposing organic substances, and therefore of possible excretal pollution.
  • The number of species of aquatic fungi is small, and of these the only one which needs consideration in relation to the purity of water supply is the association of fungi, bacteria and protozoa, commonly known as the “Sewage Fungus” which may be found in streams and rivers into which sewage effluent is discharged. 
  • The appearance presented by this growth is that of a dirty yellow or greyish jelly-like film covering the bottom and sides of the watercourse in which it occurs, and which is especially abundant where the current is slow or the watercourse tortuous. 
  • It may be found growing plentifully in drains which carry off the effluent water of sewage farms. Whenever this fungus occurs, it is certain sign of the presence in the water of a large quantity of organic compounds and, therefore, of possible pollution either with sewage effluent, or perhaps with raw sewage.

Fauna of Water Supplies

  • Members of all the chief groups of fresh water animals are to be found in one or other of the various sources from which water supplies are drawn. 
  • They may gain access to purification plants at waterworks, but rarely cause serious trouble in these. 
  • In the past, before the sand filtration of public water supplies was universally adopted , there are several instances where Sponges, Polyzoa and Mollusca are reported to have flourished abundantly in service pipes and mains. 
  • The sand filtration of water effectively excludes the minute larval stages of these animal types, which can pass readily through the strainers used to stop the grosser inclusions of natural waters. 
  • Should these larvae, on the other hand, gain access to the water pipes, they may lodge at suitable sites and develop into the adult forms. The latter feed on Diatoms and other Algae which are invariably present in unfiltered water, and may multiply so greatly as to seriously reduce the capacity of the pipes. 
  • They afford lodgment, too, to a whole host of organisms which would otherwise to swept on by the current, and when members of this pipe fauna die their decay pollutes the water and favors the growth of saprophytic bacteria. 
  • The common freshwater fishes are usually to be found in sources of water supply, such as rivers and natural lakes. 
  • They are thought to exercise a beneficial influence on the quality of the water, in that they feed on the smaller plant and protozoal forms, and so possible limit the numbers of these. 
  • For this reason, artificial impounding reservoirs for the storage of water are commonly stocked with fish, generally trout.

Bacteriological Evaluation of Water :

  • An understanding of the significance of the results obtained by the bacteriological examination of water supplies presupposes a knowledge of the possible bacterial forms which may be found in water. These forms may be broadly classified into two main groups. 
  • Firstly, saprophytic bacteria which are indigenous to water, are adapted to live and multiply at temperatures lower than body heat, e.g. at 20-220C., and derive their nutriment from decaying organic matter. These free-living forms are of little importance from the hygienic standpoint, except that their presence in a water in very large numbers denotes an abundance of organic matter. 
  • The second broad group , which may be called the adventitious water micro-organisms, are introduced from outside sources and are incapable of surviving in water for an indefinite period. 
  • Amongst these are included bacteria precipitated from the air by rain or snow, soil bacteria washed in after heavy rainfall, and excretal bacteria from human or animal sources. It is with the two last named that the microbiological evaluation of water supplies is almost entirely concerned. 
  • It has already been mentioned that the present bacteriological techniques used for the detection of sewage pollution of water supplies are directed to the demonstration of known excretal bacteria, especially organisms of the coliform group, and , to a lesser extent, faecal streptococci and Clostridium welchii. 
  • The reason for this greater concentration on the coliform bacilli is partly because of the greater ease with which they can be demonstrated by cultural methods, and partly because Cl.welchii has been found to survive considerably longer in water than members of the coliform group. 
  • The presence therefore of this organism alone in a water sample may indicate a pollution more distant in time than is the case with members of the coliform group

Coliform Bacilli 

  • The coliform bacilli constitute a group of organisms of diverse origin. Whose natural habitat is the human and animal intestine and named as Escherichia coli. 
  • Some of the coliform groups appear to have their primary habitat in the soil and on vegetation and may, therefore, be regarded as saprophytes; these comprise the E.aerogenes,and E cloacae. 
  • The typical E. coli does not normally lead a saprophytic existence outside the human and animal intestine.
  • It is the dominant organism found in faeces, and for this reason is commonly referred to as “ faecal coli,” whilst the saprophytes referred to as “non-faecal coli”. 
  • The observations of various workers suggest that at ordinary temperatures non faecal coli group tend to survive longer in water than do faecal coli, through factors other than temperature probably play a part in determining the relative length of survival of these organisms. 
  • Since E coli does not normally live for any length of time outside the intestinal tract of man and animals , the presence of this organism in water can be regarded as almost certain evidence of recent excretal pollution of human or animal origin. 
  • The further significance of the coliform group as an indication of the nature and time of pollution will be returned to later. 
  • It may be mentioned here, however, that there is no very satisfactory method at present for distinguishing between faecal coil of human origin on the one hand and those of animal origin on the other. 
  • A consideration of the topographical circumstances relevant to the water supply under examination may sometimes help in assigning faecal coli to their probable source. 
  • For example , in the case of surface waters where sheep commonly graze the gathering grounds , and in the absence of any known sources of human pollution, the faecal coli isolated from samples are in all probability of animal origin. 
  • A similar conclusion may sometimes be arrived at in the interpretation of the bacteriological findings in the case of a well or stream water, where the topographical survey on the spot indicates excretal pollution by livestock and, as far as can be seen after careful investigation, there is little possibility of contamination from human sources.

Clostridrium Welchii

  • This organism is normally an intestinal inhabitant . It is a spore-forming organism, which survives for a considerably longer time in water than the coliform bacilli, and usually resists chlorination. 
  • Its presence in water indicates that faecal pollution has occurred, and the finding of Cl.welchii in the absence of members of the coliform group indicates that the contamination is not of very recent date. 
  • The chief value of looking for this organism would seem to lie in the detection of remote or intermittent pollution in surface or shallow water supplies , such as those from a pond or a well. 
  • Supplies from these sources are commonly used on farms and by small rural communities and their frequent examination by the coliform test is seldom, if ever , practicable. 
  • An occasional examination for coliform bacilli might in any case yield misleading results, since these organisms might have died out since the last access of pollution. In circumstances such as those mentioned, then, the demonstration of Cl. welchii will show that water is subject to contamination, and will indicate the necessity of taking steps to eliminate the source of pollution, or otherwise prevent it gaining access to the water

Faecal Streptococci 

  • Streptococci of various types are present in a number of situations in the human and animal body. In human faeces the most characteristic type is that usually referred to asStr.faecalis.
  • The value of a bacteriological test for the detection of these organisms in water supplies appears to be largely undecided at the present time. Many workers are of the opinion that it adds little to the information yielded by the test for coliform bacilli. 
  • Other workers, on the other hand, believe that it has a considerable value in assisting the interpretation of bacteriological analysis when the results of the coliform test are irregular or indefinite. 
  • Thus, for example , when it is uncertain whether certain irregular types of coliform bacilli are or are not of faecal origin, the accompanying presence of faecal streptococci will constitute presumptive evidence that the irregular coliform types are derived from faeces.

The Coliform Test 

  • The bacteriological examination of water supplies for organisms of the coliform group comprises the most suitable and the most generally applicable test for evidence of pollution. 
  • The complete examination comprises a number of separate procedures by which it is possible not only to demonstrate the presence of coliform bacilli, but also to assign them to the sub-groups already mentioned. 
  • The complete test for coliform bacilli comprises the following procedures (i) the presumptive coliform count, (ii) the differential coliform test, and plate counts at 220C and 370C. 
  • The particular test or combination of tests required for any given sample submitted for examination will be decided by the bacteriologist after consideration of the relevant details pertaining to the circumstances under which examination of the water supply in question became necessary. 
  • The importance of supplying as full particulars as possible when forwarding samples to a laboratory for examination can, therefore, be readily understood. 
  • By the plate counts at 220C and 370C, the total number of viable bacteria per unit volume of water is determined. Most of the bacteria growing at 220C , are saprophytic types which are non-pathogenic to human beings or animals. 
  • It may be thought that the plate count at 220C, is immaterial; to come extent this is true, but it may be pointed out that this count affords some indication of firstly the amount of food substance available for bacterial nutrition, and secondly the amount of soil, dust and other extraneous material carrying bacteria with it that has gained access to the water. 
  • On general grounds the greater the number of organisms developing at this temperature, the larger is the amount of available organic matter present, and the less suitable is the water for human consumption. 
  • The bacteria developing at 370C on the other hand, are mainly parasitic or potentially parasitic, though not necessarily pathogenic, types derived from soil, sewage or excretal material , and must therefore be regarded as evidence of the possible presence of pathogenic types such as members of the typhoid , paratyphoid group. 
  • The presumptive coliform count, together with the differential coliform test, is by far the most delicate index of excretal pollution. These tests are carried out on a quantitative basis and the results reported, according to the most recent recommendations, in the following manner #Probable number of coliform bacilli present in 100 ml.  #Probable number of faecal coli present in 100 ml.

Interpretation of Bacteriological Examination

The interpretation of the results of the bacteriological examination for coliform bacilli, as well as those for the other intestinal bacteria, calls not only for careful consideration of all the relevant factors, but also for considerable experience in this work. 

Final decisions have yet to be reached as to the meaning of all the data obtainable in the laboratory, and any conclusions reached must still be to some extent reflections of individual experience and , therefore , variable. 

The bacteriological condition of a water, too , has to be considered in relation to many other factors such as season, nature and topography of the source of supply, the frequency of examination, etc. 

The following quotations give the most authoritative information available at the present time regarding the interpretation of results and the hygienic classification of water supplies 

  • E. coli is essentially an index of recent excretal pollution. The finding of this organism in water in more than minimal numbers can never be safely ignored. 
  • The presence of organisms of the saprophytic group in water in the absence of faecal coli may be due either to (a) contamination of the water with soil; (b) contamination of the water with excretal material at a time sufficiently distant to allow faecal coli to die out; (c) Contamination of the water with the excreta of a person who is discharging the saprophytic organisms in almost pure culture; this must be relatively uncommon; (d) inadequate treatment of an initially polluted water with chlorine; which has only succeeded in killing off the more susceptible faecal coli. Which of these explanations is correct can be determined only by inquiry into the source and history of the water. 
  • The finding of a high proportion of faecal coli among the total coliform organisms is indicative of heavy or recent excretal pollution. On the other hand, a result showing that the majority of the coliform organisms appear to belong to saprophytic group , or to irregular types may be regarded as indicative of a slight, infrequent, or remote excretal pollution; or perhaps if no faecal coli are present at all, of simple contamination with soil that may or may not have been excretally polluted some time previously. 
  • In practice it is unwise to neglect completely the presence of organisms of the saprophytic group. Even though no faecal coli can be found , their presence may indicate a minor degree of pollution which at any time might become serious. Their appearance in a water, particularly a deep well water, from which they are normally absent, sometimes heralds the advent of pollution and enables steps to be taken in time to stop further pollution or , if this is impossible, to protect the consumer by suitable treatment of the water. 
  • In general terms, the presence of faecal coli denotes recent and possibly dangerous excretal contamination, which must be urgently attended to. The presence of saprophytes in an untreated water suggests less recent contamination, which though not immediately dangerous is nevertheless sufficient to call for further steps towards obtaining greater purity of the supply. The presence of saprophytes in a treated water suggests either inadequate treatment or the access of undesirable material to the water after treatment.

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