CHAPTER TWO: LITERATURE AND CONCEPTS REVIEW
II.1. Generalities on waters
According to Maurice B. ’’water is a complex molecule which is not only composed by oxygen and hydrogen, but contains also suspended solids, dissolved chemical compounds, microorganisms, and bacteria either pathogenic or not to the life of animals and human.’’
The scientist VAILLANT. J. precise that the term “water” is applied on the black waste water from the industry as well as on clean water from sources which is colorless and tasteless also on water which cannot be consumed of the oceans as well as the potable water mostly available and attractive to human beings.
II.2. Sources of water
The classification of water can have variable bases according to specialties like chemistry, medical, geology, engineering and so on.
But in general we have four (4) common sources of water: (i) rainwater, (ii) surface water, (iii) ground water, (iv) water obtained from reclamation.
II.2.1. Rainwater
In this type of water, we distinguish water from roofs and dwellings which is stored in small underground tanks or cisterns for small individual supplies and water obtained from prepared catchments, so by sloping the ground, that water may be stored in moderate reservoirs and is used for communal supplies mostly for drinking purposes.
II.2.2. Surface water
Surface water is the one which is available as runoff from catchments area during rainfall or precipitation; it can be stored in the reservoirs by constructing a dam across it or be diverted into water supply channel. We obtain surface water from rivers by continuous draft, river diversion and reservoirs storage of intake from natural lakes.
II.2.3. Ground water
The term “ground water” refers to the water which is stored by the natural undergrounds in the water bearings formation of earth trust. The ground water
reservoir consists of water held in voids within a geological stratum. We have then natural springs, well and bore hores, in infiltration galleries etc.
II.2.4. Water obtained from reclamation
Saline or blackish water may be rendered useful for drinking purposes by installing desalination plants. Also effluents or waste water can be treated suitably so that it may be reused. So, those kind of water gives water called ‘’water obtained from reclamation’’.
II.3. The water cycle
The water cycle is the process of transferring moisture from atmosphere to earth in the form of precipitation, conveyance of precipitated water by streams and rivers to oceans, lakes, etc. and evaporation of water back to the atmosphere .
Figure1: Water cycle in nature
As illustrated by the above diagram the water cycle consists of the following processes:
-Evaporation and transpiration: In this phase, water from surface of oceans, lakes, rivers and also from moist soil evaporates; the vapors are carried over land by air in the form of clouds. However, the transpiration is the leaving of water from leaves of plants through their pores.
-Precipitation: It is the fall of moisture from the atmosphere to the earth surface in any form.
-Runoff: The part of water not evaporated, runs to the oceans trough surface or subsurface streams.
So, all the above mentioned processes complete the water cycle.
Briefly, water evaporates from water bodies and by transpiration it leaves the plants then goes in the atmosphere in clouds form, after losing some of its properties, it falls as precipitation, then some evaporates, other infiltrate. Finally the rest of water runs to the oceans and it forms the natural cycle of water.
II.4. Types of water
According to its utilization, water is subdivided into:
1) Potable water: is water which fulfills physico-chemical and bacteriological characteristics and responding to all physiological needs of human beings.
2) Industrial water: is a kind of water that is used in different chemical industries, like breweries, etc. It gets special treatments its use (before being used).
3) Residual water: is a kind of water that has been used like in bottle cleaning or fabricated products; that water has been polluted by chemicals used in the fabrication or used for good cleaning services.
II.5. Characterization of water
II.5.1. Physical parameters of water
II.5.1. 1. Color
The potable water has to be limpid or colorless. Its color comes from the substances in solution like dissolved matters and suspended ones. Other dissolved substances may add their own coloration (e.g.: iron and manganese). But there is no correlation between color and organic matters concentration.
II.5.1. 2. Temperature
The temperature plays a significant role in solubility of substance especially of salt and gases and in density determination. It influences then the electrical conductivity and pH value of water, Furthermore, if its elevation is more than 15oC favors the development of microorganisms in water.
II.5.1. 3. Taste and odor
The taste and odor of water come from the reagents mixed with it. They may also be developed while storing or distributing. They are just the pollution indicators. It has to be noted that clean water has to be tasteless and odorless and its odor and taste can be evaluated by two persons.
II.5.1.4. Turbidity
The turbidity proves the presence of suspended matters. The potable water doesn’t have to be troubled. The turbidity has to be eliminated for improving the esthetic part of water, allows a good disinfection and avoids the eventual deposition of matters in distribution network. If water is strongly troubled, there is a risk that microorganisms can fix themselves on particles in suspension.
In turbidimetry, we compare the turbidity of a given sample with that of reference suspension constituted by formazine.
The unity of turbidity is NTU (Nephelometric Turbidity Unity).
Table 1: Classes of usual turbidities
| Value of turbidity in NTU | Water quality |
| NTU<5 | Clear water |
| 5 | Water softly troubled |
| 30 | Troubled water |
II.5.1. 5. Suspended solids
The suspended solids are inorganic salts and organic matters; their degree of polluting water depends on sources of water (domestic, industrial, runoff water). The total solids in the solution have an important effect on the taste of drinking water.
II.5.2. Chemical parameters
The mineralization of water in general is heavy for underground water and surface water and surface water. It is estimated by using the following parameters: conductivity, pH, complete alkalinity titration (TAC), simple alkalinity titration (TA), ammonium
, free CO2, Fe, Mn, Zn,…
II.5.2. 1. Conductivity
Conductivity is the measure of the resistance opposed to electrical current. It constitutes a measure of dissolved matters contained in natural water; where less concentration of dissolved elements are complementally ionized and contribute to the conductivity.
Table2 : Quality of drinking water in function of conductivity
| Conductivity (µs cm-1) | Quality |
| 50-400 | Excellent |
| 400-750 | Good |
| 750-1500 | Poor |
| > 1500 | Excessive mineralization |
II.5.2. 2. pH
The pH parameter has got a definition as a measure of hydrogen ion concentration in water
. It is a very useful parameter because it indicates if water is acidic or basic (alkalinity). So, is very important for determination of aggressivity of water. It is a very good operational parameter for the quality of water.
II.5.2. 3. Hydrotimetric titration (TH: Hardness)
The hydrotimetric titration (TH) expresses globally the concentration in salt of calcium and magnesium dissolved. These substances are the main causes of hardness in water supply system
The water with elevation of TH is called “hard’’ and “soft’’ for the lower TH
We can distinguish:
-The temporary hardness which comes from the combination of ions of calcium and magnesium with carbonates and bicarbonates ions.
-The permanent hardness or non carbonates hardness which comes from the combination of some ions with sulfates and chloride ions
II.5.2. 4. Calcium titration (Tca)
The hardness of water is due to the presence of dissolved calcium and magnesium. The following allowable detection of calcium water is100 mg/l to
300mg/l limits.
The hardness which is superior to 300mg/l can cause problem in distribution systems like deposition of calcium carbonates.
So, the titration of calcium (Tca) has an objective of knowing how much calcium is in the examined water.
II.5.2. 5. Alkalinity
The value of TA and TAC allow to the operator to know hydroxides dosage, carbonates, and alkalines contained in water. They are dosed by using sulfuric acid and phenolphthalein as indicators for TAC.
-The simple alkalinity titration (TA) measure the totality of the
and 
ions only.
-The complete alkalinity titration (TAC) measures all the ions such as:
,…
In the case of potable water, the ion concentration is very low and negligible. So, the alkalimetric titration has the objective of knowing the capacity of water to neutralize the acid. It is then the determination of bicarbonates and hydroxide contents, therefore the alkalinity is the concentration of these compounds in water.
II.5.2. 6. Nitrates, nitrites and ammonium
a) Nitrates: some water contain nitrates at its natural state, those substances can be introduced directly and indirectly in water:
-by non treated water
-by the effluent of waste water epuration
-by the unstable liquid wastes
The nitrates are very toxic when are found in excessive concentration in drinking water can cause some blood problems to consumers. It may also cause cancer to the old persons who consume that kind of water.
b) Nitrites: the presence of nitrites in water is due to the reduction of nitrates or the microbial oxidation of the ammonium. They are easy oxidized in nitrates; their presence in water distribution system requires bacteriological and medical analyses. The excess of nitrites in water can cause the heart problems.
c) Ammonium: is a gas which may be soluble in water, in favorable conditions of pH, it can be transformed as shown by the reaction below.
II.5.2.7. Sulfates and chlorides
In the natural water, we cannot have the strong acid free, there is only the salts derived from those acids. Sulfates and calcium, magnesium and sodium.
a) Sulfates: the presence of sulfates in water can come from the effluent of the industrial wastes and the depositions of atmospherically origin substances, but the very high concentration are found in underground waters, and they are of natural sources principally of the dissolution of gypsum (CaSO4.2H2O) and the oxidation of sulfides. The sulfate ion is one of anions which are less toxic but its high concentration can cause the problems in the human body.
b) Chlorides: their presence in water is due to natural sources, it proves the pollution by the industrial wastes. The presence of chlorides in a very big quantity in water favors the mental corrosion especially when water is poor in calcium bicarbonates.
II.5.2. 8. Iron and manganese
a) Iron: the iron is one of the very abundant metals in the world. It is found in natural waters in the concentration of 0.5mg/l to 50mg/l.
b) Manganese: as the iron is one of the abundant metals in the world. it is found near the iron on the periodic table of the elements. Till now, it has not yet been proven scientifically that the utilization of water containing manganese has any toxic effects
II.5.2. 9. Zinc
The zinc is an element very present in foods and potable water in salt forms or organic complexes. The water from taps may contain the zinc in a very big amount due to dissolution of zinc in the pipes.
10) Dissolved oxygen
The oxygen is the substance whose concentration is very useful in controlling water to be distributed. Its concentration depends on temperature of raw water, its composition, the treatment that it has gotten and chemical or biological processes that happened during distribution. The presence of distributed water to be distributed cannot be considered as bad, because it does not have any toxic effect; so, it increases the potability of water. However when the distributing systems (pipes) are made up of metal, the dissolved oxygen may be bad because it may cause the corrosion.
11) Organic matters in water
This expression refers to all substances that can be oxidized by the potassium permanganate
. Certain organic matters influence the color and the taste because they favor the development of algae and bacteria at the side of canalization systems.
The water which contains many organic matters is subjected to biological and chemical contaminations.
By doing test of organic matters, we measure the liberated oxygen in well conditions of acidity, time and temperature by using KMnO4 (Potassium permanganate)
12) Carbon dioxide
The carbonic gas is found in all ground waters and generally in very little concentration (10mg/l), but it is very high in underground waters. It does not have any bad effect on the health of human being but its high concentration cause corrosion of pipes in the water distribution system.
II.5.4. Bacteriological parameters of water
The bacteria are the living microorganisms, pathogenic or not, present in nature, their presence in water diminishes its aptitude to certain utilizations. In this study we will be interested on utilization linked to the consumption by human beings. That is a why the bacteriological quality of water is particularly very important.
Pathogenic play a significant role in hygienic quality evaluation of water; when they are present in water, their number has to be reduced and their presence proves the degree of pollution. Yet, protective measures have to be taken into consideration.
- Microbial indicators of water quality
The danger that drinking water has to face is the recent contamination of waste water or by human excrement.
The micro-organisms currently used as pollution indicators are:
- Total germs
- Feacal coliforms
- Feacal streptococcus
a) Total germs
They are microorganisms in stick forms, able of growing in aerobical conditions in 36OC. The total germs are considered for long time as a good microbial indicator of quality of drinking water; because they are easier to be detected and to be counted in examined samples.
b) Fecal coliforms
They are the coliforms which have the same properties as the total germs but their incubation is done at 44oC. among those coliforms we can mention the Escherichia coli because it can eventually become pathogenic
The Escherichia coli is very abundant in human excrements and animal wastes where it can reach the concentration of 109 colonies/gram of fecal matters.
c) Fecal streptococcus
This term means generally streptococcus present in the human excrements and animal wastes.
They are also practically the specific indicators of human fecal pollution. Certain species and sub species can be found principally on vegetation. The specific objective of water quality control is to know the treatment efficacy.
II.6. Water pollution
The term water pollution is referred to the addition of an excess of material or heat that is harmful to humans, animals or desirable aquatic life or otherwise cause significant departure from the normal activities of various living communities in or near bodies of water.
The national water commission stated (1973) that water gets polluted if it has been not of sufficient high quality to be suitable for the highest uses that people wish to make of it at present or in the future.
II.6.1.Classification of water pollutants
The signs of water pollution have been obvious to even the most casual observers to aid in systematic discussion of water pollutants, they are classified into 9 categories given below:
1. Oxygen-demanding wastes
2. Disease causing agents
3. Plants nutrients
4. Synthetic organic compounds
5. Oils
6. Inorganic chemicals and mineral substances
7. Sediments
8. Radioactive materials
9. Heat (thermal pollution)
- Oxygen-demanding wastes
Dissolved Oxygen DO has been a fundamental requirement of life for the plants and animal population in any given body of water, their survival is dependent upon the ability of the water to maintain certain minima concentration of this vital substances. A body of water has been classified as polluted when the DO concentration drops below the level necessary for sustaining a normal biota for that water.
Although some inorganic substances occur in this category, most Oxygen-demanding wastes are organic compounds. Pollutants in this category typically comes from such sources as sewage, both domestic and animal industrial wastes from food processing plants, wastes from paper mill activities, tanning operation, by products, effluents from slaughterhouses or meat-packing plants.
Most compounds involved in this type of pollution have carbon as their most abundant elements. One reaction undergo, with the bacterial help, is the oxidation of carbon.
C+O2 CO2
As Oxygen-demanding wastes rapidly deplete the DO water, it has been impossible to estimate the amount of these pollutants in a given body of water. The Biological Oxygen Demand (BOD) of water has been quantity related to the amount of wastes present. In a given sample, the BOD indicates the amount of dissolved oxygen used up during the oxidation of oxygen-demanding wastes. It could be found out by incubating a sample of water at 20o C. The amount of oxygen consumed (BOD) could be found out by chemical determination of the DO concentration of the water before or after incubation and it is measured in ppm.
A BOD of 1ppm has been a character of nearly pure water. Water has been regarded fairly pure with BOD of 3 ppm and doubtful purity when the BOD value reaches 4 ppm.
- Disease causing agents
Water has been a potential carrier of pathogenic micro-organisms and can endanger health and life. The pathogens most frequently transmitted through water have been those responsible for infectious of the intestinal tract (typhoid and para-typhoid fever, dysentery and cholera) and those responsible for polio and infectious hepatitis. The responsible organisms are present in the feces or urine, infected people and are ultimately discharged into a water supply.
Waste water released from municipalities, sanitaria, tanning and slaughtering plants and boats may be sources of bacteria and other microorganisms which are capable of producing diseases in men and animals including livestock. Any fair sized community at any given time has been likely to have some persons who are diseased so that microorganisms are almost always present in sewage.
The identification of microorganisms in water needs very large samples many sophisticated techniques and is too time consuming and expensive for routine pollution tests . the standard method involves determination of the most probable number (MPN) of coliforms in water sample.
- Plant nutrients
Nutrients are important limiting factor in the growth of all plants. With all other factor factors equal, the rate and profuseness of plant growth are proportional to the of nutrients available
Plants nutrients (phosphorus and nitrogen) enter fresh water and marine system and lead to or intensify eutrophication of these systems. These nutrients tend to accumulate in ground water since it is out of the eutrophic zone. As the ground water moves laterally and reaches the surface waters, these material add to the nutrient level already present.
Plants nutrients like nitrogen and phosphorus are able to stimulate the growth of aquatic plants which get interfere with water used later decay to produce disagreeable odor and add to the BOD of water. The enrichment of water with nutrients is a naturally occurring biological process called eutrophication and this enrichment lead to other slow process collectively referred to as a natural aging of lake. The steps in eutrophication and aging lake have been as follow:
- Streams from a drainage basin gradually bring soil and nutrients to a newly formed lake, increasing the fertility of the lake water.
- The increased fertility leads to an accumulating growth of aquatic organisms, both plants and animals.
- Plants take root of the bottom and gradually occupy more and more of the space. Their remains accelerate the filling of the basin.
- The lake gradually becomes marsh and finally a field or forest as it has been overrun by vegetation.
The time needed for this aging process to be completed could be measured in thousands of years. The actual time depends upon the size and mineral content of the basin and the climate.
- Organic chemicals
The exotic organic chemicals include surfactants in detergents, pesticides, various industrial products and the decomposition products of other organic compounds. Analysis of polluted water reveal the presence of a wide variety of these compounds. Some of these compounds have been found to be toxic to fish at very low concentration such as 1ppm phenol. Many are not biologically degradable or are degradable only very slowly.
Laundry detergents, a common constituent of waste water has been another organic contaminant. Detergents can become a problem as they are not readily broken down by bacterial actions and have a long residence time. Even in relatively low concentration, they can cause water to form foam .
Hydrocarbons, in the form of gasoline and motor oil , although insoluble in water, have been carried from roadways and parking areas in the rain water runoff. In addition to the substance mentioned above, analysis of water reveals the presence of a wide variety of other organic chemicals. Some of these compounds are known to be toxic at very low concentration, while many are not biodegradable or break down very slowly.
- Oils
The production, distribution and use of such large yearly quantities result in some oil contamination of the environment. Some of this contamination is a accident, some is not.
- Inorganic chemicals and mineral substances
This category of water pollutants have been including inorganic salts, mineral acids and finely divided metals or metal compound such as methyl mercury (
), iron pyrite (
), etc. these substances enter natural water because of various activities in various smelting, metallurgical, chemical, industrial, mine drainage and various natural processes. The presence of this bring about three general effects: the acidity, salinity and toxicity of may be increased.
Inorganic chemicals of many types enter water from municipal industrial waste waters and runoff. These pollutants are able to kill or injure fishes and other aquatic life and they can interfere with suitability or water for drinking or industrial use. Many of these inorganics are not only toxic but tends to concentrate in food chain.
- Sediments
Sediments are soil and mineral particles which are washed from the land by storms and flood waters, from cropland, unprotected forest soils, overgrazed pastures, strip mines, loads and bulldozed urban areas. Sediments are able to fill stream channels and reservoirs: erode power turbines and pumping equipments: erode power turbine and pumping equipments: reduce the amount of sunlight available to green aquatic plants plug water filters and blanket fish nest, spawn and food supplies thus reducing the fish and shellfish population.
Sediments are almost regarded as a type of pollution due of the natural occurring process of erosion. Sediments produced by that process represent the most extensive pollutants of surface waters have been at least 700 times as long as the solid loading from sewage discharge.
- Radioactive materials
Harmful radiations may result in water environment from the wastes of uranium and thorium mining and refining from nuclear power plants and from industrial, medical and scientific utilization of radioactive material.
Many radioactive material substances are lethal at relatively low concentration and minute amount may be mutagenic. Perhaps the greatest problem of radioactive pollution as a result of uranium production has been caused by large quantities of “uranium tailings” produced. This finely divised solid material remains after usefull material have been leached out. Huge piles of these tailings are found in uranium producing areas. These tailings create a radioactive pollution problem as they contain radioactive decay products of uranium. Two of these radioactive material are Thorium-230 (
) and Radium-230 (
).
There are four types of pollutants that are formed by nuclear generating plants:
(a) Low level radioactive liquid wastes: radioactive substances are produced when impurities in the primary coolant water and corrosion products from the coolant pipes are bombarded with neutrons from the core area. This can be avoided to some degree by using demineralized coolant water.
(b) Heat: The secondary cooling system takes away huge amount of heat from the reactors and mixes it into water supply.
(c) Liquid and gaseous waste from fuel elements: complete sealing of the fuels in steel or zirconium container is apparently impossible to attain or sustain. Minute cracks allow fission products to escape into the primary coolant, this further complicates the disposal problems of law level waste.
(d) Fission products: within 1-3 years fission products (the ashes of nuclear fuels) accumulate to the point that they absorb sufficient neutrons to slow or stop the chain reaction.
- Heat (thermal pollution)
Vast amount of water find use for cooling purposes by stoamelectric power plant (and other industries to a lesser extent) cooling water is discharged at a raised temperature and some rivers may have their temperature so high (even up to 40oC ) that fish life completely gets eliminated and the lake or river becomes useless for assimilation or pollution further cooling
Increasing the water temperature of system is harmful since it generally alters the chemical, physical and biological characteristics of the system. In addition to the possibility of decreasing the amount of dissolved oxygen in the water and increasing the rates of chemical reaction.
II.7. Sources of contamination of water pollution
The major sources of water contamination are domestic, industrial, agriculture waste water, solid waste thermal pollution, shipping water pollution and radioactive waste.
II.7.1. Domestic water
Includes waste water from homes and commercial establishment. Domestic water arises from many small sources spread over fairly wide area but it is transmitted by sewers to a municipal waste treatment plant. This water is largely organic and gets oxidized by bacterial decomposition to nitrates, phosphates, CO2 and H2O. as this type of decomposition needs the use of dissolved oxygen, it places an oxygen demand on the system. Because of this tendency to remove the oxygen in the decomposition process, a common indicator used to monitor this type of input in receiving water is the BOD (Biological Oxygen Demand) test
II.7.2. Industrial water
This occur in large amount in specific locations making collection and treatment fairly simple to accomplish. There are water-using factories which are discharging water with a total BOD load about 3 to 4 times as large as the load from sewed population. Only about 7 or 8% of industrial waste waters are disposed of in municipal sewer system.
II.7.3. Agricultural water pollution
It include sediments, fertilizers and farmanimal wastes. This pollutants can all enter waterways as runoff from agricultural lands but farm animal wastes are an especially large problem near the large feedlots on which thousands of animals are concentrated.
Agricultural wastes includes the pesticides that are sprayed on crops, as well as sediments, fertilizers, plant and animal debris that are carried into water ways during periods of rainfall or as runoff and during the irrigation of farmland waste generated by farm animals are also included in this category. The practice of keeping large number of animals in small area has lead to an excess of animal waste generated in and confined to a given area where it has been economically important to distribute wastes for reuse as fertilizers. These material become problem when they are allowed to enter waterways during the cleaning of the confinement areas or during periods of heavy rainfall when runoff carries them into adjacent waterways. Since these wastes are organic they increase the BOD of receiving wastes.
II.7.4. Solid waste water pollution
Solid waste varies in composition with socioeconomic status of the generating community. The following material could be classified as solid waste:
a) Garbage which include all decomposable wastes from households, as well as from food canning, freezing and meat-processing operation that are not disposed of in waste waters.
b) Rubbish includes all non decomposable wastes. These material may be either combustible and non combustible. Combustible material would include garden wastes, cloths, papers, etc. Non combustible material include masonry, some chemicals, material and glass.
c) Sewage sludge is generated from settling processing in primary, secondary and tertiary treatment methods as well as the solid from cesspools which must be removed periodically
d) Miscellaneous material include industrial wastes like chemical, paint and explosive as well as mining waste such as slag heaps and mine tailings.
II.7.5. Thermal pollution
Thermal pollution takes place because of many electric generating companies that use water in the process of cooling their generators. This heated water is released into system from which it was drawn, causing a warming trend of the surface waters. The pollution result when the heated effluent is released into a poorly flushed system. In these cases the temperature increases often result which tends to decrease the solubility of dissolved oxygen.
In lakes, it also becomes possible to bring about nutrients redistribution and and prolong summer stagnation periods.
II.7.6. Shipping water pollution
It include both human sewage and other wastes. The most important of this pollution is oil. Oil pollution result from the accident involving oil tankers and from spills at offshore oil drilling sites. A more persistent source of oil pollution result from the practice of oil tanker, after they deliver the oil, to fill the empty tanker is discharged. Although this practice is illegal, it is difficult to prevent. The alternative is to pump the contaminated sea water into tanks at port, this is not only inconvenient but uneconomical. In additional there will remain the problem of disposal when the disposal tanks are full.
II.7.7. Radioactive waste pollution
The major sources of radioactive waste is nuclear explosive accent at nuclear power plant, fuel processing plants, and research laboratories and hospitals that are release these wastes into the atmosphere or into the waste water. Presently most interests centers on radioactive iodine and strontium, since the man is at the end of food chains that concentrate these elements.
Table 3: The principal pollutants of water and their origin
| Pollutants | Origin |
| 1. Sediments | Land surface, pavement and vehicle wear (tyres, brakes), atmosphere, spillage, illegal discharge, organic matters (leaf, grass, droppings), runoff water from washing cars, weathering of building structure. |
| Organic matters, fertilizers, sewer overflows (septic tanks leaks), animal (birds droppings ), detergents (car washing), atmosphere and spillage. |
| Decaying organic matters, atmosphere, sewer overflows, animal dropping and spillage. |
| Animal droppings, sewer overflows and organic matters. |
| Atmosphere, spillage and decaying organic matters. |
| Pesticides, herbicides, spillage sewer overflows, weathering of buildings and spillage. |
| Atmosphere, Vehicle wear, overflow, weathering of building, spillage. |
| Asphalt pavement, spillage (illegal discharge), leaks from vehicles, car washing and organic matters. |
Source: UWAMAHORO Félix, KIST, Research project 2003
II.8. Water standards used in Rwanda
There are a number of physical, chemical and bacteriological international standards for potable water quality in existence. So, We distinguish the following agencies that gave different types standards of standards of quality water:
- World Health Organization (WHO)
- United States Public Health Society (USPH)
- United States Environment Protection Agency
- Indian Council of Medical Research (ICMR) Committee
- American Water Works Association (AWWA)
- Environment Hygiene Committee, etc
In our research, We shall be using those established by WHO because is less obliging than others, even RECO & RWASCO ( the former ELECTROGAZ) uses those standards of WHO.
In 1992, the government of Rwanda thru Ministry of public works, water and sanitation (MINITRAPE) dared to determine the quality of water standards in Rwanda, but it has done for some parameters.
Standards of drinking water according to WHO
A) Table 4: Elements to be controlled
| Elements | Units | Limits of concentration |
| mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l Ptco mg/l Celsius degrees
FTU mg/l mg/l mg/l mg/l mg/l colonies colonies colonies colonies | 0.005 5 5-20 0.05 100-300 0.5 1.5 50 75 0.05 30 0-0.01 0.015 5 200 0.05 5 6.5-8.5 0-5 0.1-5 25 100-200 0-5 0-2 0.2-0.4 500 10-20 5 300/ml 0/100ml Any in 1000ml Any in 5000ml |
Source: UWAMAHORO Félix, KIST, Research project 2003
B) Table 5: Toxic substances
| Substance | Limits of concentration (mg/l) |
| 0.10 0.05 0.01 0.05 0.05 0.01 1.00 |
Source: UWAMAHORO Félix, KIST, Research project 2003
C) Table 6: Rwandan Standards published by GTZ/ MINITRAPE (DEA) 1992
| Parameter | Non treated water concentration | Treated water concentration |
| Total germs Fecal coliforms pH Specific conductivity Nitrites Nitrates Ammonium Residual chlorine |
0 colonies/ ml 4 – 9
<1.0> <80 mg/ l <2.5> _ | <100> 0 colonies/ ml 6.5-8.5 _ 0.5 mg/ l 50 mg/ l _ >0.05 mg/ l
|
Source: UWAMAHORO Félix, KIST, Research project 2003
