Water is defined as a chemical substance eith the chemical formula H2O(Two hydrogen atoms covalently bondend to one oxygen atom. Water exists in the liquid state in ambient conditions and co exists in solid state also as ice and in the gaseous state as water vapour or steam. Water covers 70.9% of the Earth surface(Ocean). 98% water found on the Earth planet is in the ocean,thus usuable for drinking purposes because of the salt. About 2% of the planet's water is fresh,but 1.6% is locked up in the polar ice caps and glaciers. Another 0.36% is found underground in aquifer and wells. Only 0.0036 % of the whole planet's total water supply is found in lakes and rivers. The rest of the water is found on the planet either floating in the air as clouds and water vapour or locked up i the plants and animals.
hydrological cycle
Local context,No of reservoirs etc map of big rivers.
In the local context that is in Mauritius,it is the Central Water Authority (CWA) which controls the water treatment and distribution of potable all over the island. The CWA is a parastatal body functioning under ages of the Ministry of Public Utilities.
Map of mauritius with all rsevoirs and main rivers
Main source of water supply comes from the ground water which is of about 54%.
2.
Uses of water drinking irrigation industrial
3.
Quality of water
The quality of water is very powerful environmental detreminant of health. The safety of drinking water lead to the prevention and control of waterbornes diseases. Water is vital to li human life. Water is important to human for drinking purposes, for crops to grow and also for animal consumption. Water can be considered as a "food" for all living organism on the whole world. But water is considered as a major vehicle for the spread of infection and a safe water supply isessential for health.
Polluted water is important for the spread of Esch.coli enteritis,which may indeed be the commonest form of watreborne enteritis. Water infected with microbes can lead to serious health problems such as diarrhea,poliovirus,hepatis A & E in human. A complete hygienic and strict sanitation systems can maintain a good water quality.
Parameters to be analysed
Coliform
Coliform bacteria are very common water pollutant. They are originated from the guts of ruminat animals such as cattle. Coliform is also present in the faeces of such animals. The good news is that coliform bacteria is not particularly hazardous to health. Most health institutions will consider water less than 5 CFU's safe to consume. But still the drinking watre is tested for the presence of coliform as it indicates the existence of the possible pathways through which a water suppply can be contaminated with animal waste. The animal waste can give rise to a significant number of very dangerous organisms into a water supply. In short coliform bacteria is used as an indication of possible futere contaminants by a much more dangerous group of bugs.
Faecal coliform
Faecal coliforms are primarily Escherichia and klebsiella spp. They are distinguished from the total coliform by having the ability to ferment lactose at elevated temperatures and as well as 35 degrees celcius, the optimun temperature for coliform. The elevated
E coli
TVC
BOD
Biological oxygen demand is a measure of the quantity of oxygen which is taken up by microorganismd(e'g aerobic bateria)in the oxidation of organic matter. Plant decay and leaf fall sre natural sources of organic mattter.Urban runoff carries pet wastes from streets and sidewalks; nutrients from lawn fertilisers, persticides and insecticides; leaves, grass clippings, and paper from residential areas, which increase oxygen demand. Oxygen consumed in the decomposition process robs other aquatic organisms of the oxygen they need to live. Organisms that are more tolerant of lower dissolved oxygen levels may replace a diversity of natural water systems contain bacteria, which need oxygen (aerobic) to survive. Most of them feed on dead algae and other dead organisms and are part of the decomposition cycle. Algae and other producers in the water take up inorganic nutrients and use them in the process of building up their organic tissues.Consumers like fish and other aquatic animals eat some of the producers, and the nutrients move up the food chain. When these organisms die, bacteria decompose the organic compounds and release into the water inorganic nutrients such as nitrate, phosphate, calcium, and others. Some of these nutrients end up down stream or in sediments, but most of them recycle again and again. Most of the bacteria in the aquatic water column are aerobic. That means that they use oxygen to perform their metabolic activities of decomposition. Remember that we learned in other related exercises that under normal conditions, dissolved oxygen exists in very low concentrations. Natural levels of oxygen in aquatic systems are always somewhat depleted by normal levels of aerobic bacterial activity. In most cases, if dissolved oxygen concentrations drop below 5 parts per million (ppm), fish will be unable to live for very long. All clean water species such as trout or salmon will die well above this level and even low oxygen fish such as catfish and carp will be at risk below 5 ppm.
COD
Chemical oxygen demand (COD) is used as a measure of oxygen requirement of a sample that is susceptible to oxidation by strong chemical oxidant. The dichromate reflux method is preferred over procedures using other oxidants (eg potassium permanganate) because of its superior oxidizing ability, applicability to a wide variety of samples and ease of manipulation. Oxidation of most organic compounds is 95-100% of the theoretical value
pH
pH indicates the level of acidity or alkalinity of a liquid(water,juice,soft drinks). Basically the pH value determine whether the water is hard or sofl. The pH of pure water is 7. Generally, water with the pH greater than 7 is considered to be alkaline(basic) and water with pH less than 7 is considered as acidic. The normal range for pH of surface water system is 6.5 to 8.5. The maesurement of pH is needed to determine the corrosiveness of the water. Water with low pH can be <
6.5(acidic,soft corrosive). This means that water can contain metal ions such as manganese, copper, lead, zinc or other high level of toxic metals.
This can cause premature damage to metal piping, and have associated aesthetic problems such as a metallic or sour taste, staining of laundry, and the characteristic "blue-green" staining of sinks and drains. More importantly, there are health risks associated with these toxins. The primary way to treat the problem of low pH water is with the use of a neutralizer. The neutralizer feeds a solution into the water to prevent the water from reacting with the household plumbing or contributing to electrolytic corrosion. A typical neutralizing chemical is soda ash. Neutralizing with soda ash, however, increases the sodium content of the water.
Water with a pH > 8.5 could indicate that the water is hard. Hard water does not pose a health risk, but can cause aesthetic problems. These problems include an alkali taste to the water (making that morning coffee taste bitter), formation of a deposit on dishes, utensils, and laundry basins, difficulty in getting soaps and detergents to lather, and formation of insoluble precipitates on clothing.
Electrical conductivity
Generally water which is chemically pure should not be a conductor of eletric currents. Any increase in electrical conductivity in drinking water indicates the presence of electrolytes in the form of pollution(Angell,1982). Electrical conductivity is directly related to the temperature of the water. As temperature of water rises the electrical conductivity of water increases as well. Electrical conductivity is a direct indicator of concentration of total dissolved ions in water.
Temperatue
Heavy metal
Toxic metals can be present in industrial, municipal, and urban runoff, which can be harmful to humans and aquatic life. Increased urbanization and industrialization are to blame for an increased level of trace metals, especially heavy metals, in our waterways. There are over 50 elements that can be classified as heavy metals, 17 of which are considered to be both very toxic and relatively accessible. Toxicity levels depend on the type of metal, it's biological role, and the type of organisms that are exposed to it.
The heavy metals linked most often to human poisoning are lead, mercury, arsenic and cadmium. Other heavy metals, including copper, zinc, and chromium, are actually required by the body in small amounts, but can also be toxic in larger doses.
Heavy metals in the environment are caused by air emissions from coal-burning plants, smelters, and other industrial facilities; waste incinerators; process wastes from mining and industry; and lead in household plumbing and old house paints. Industry is not totally to blame, as heavy metals can sometimes enter the environment through natural processes. For example, in some parts of the U.S., naturally occurring geologic deposits of arsenic can dissolve into groundwater, potentially resulting in unsafe levels of this heavy metal in drinking water supplies in the area. Once released to the environment, metals can remain for decades or centuries, increasing the likelihood of human exposure.
In addition to drinking water, we can be exposed to heavy metals through inhalation of air pollutants, exposure to contaminated soils or industrial waste, or consumption of contaminated food. Because of contaminated water, food sources such as vegetables, grains, fruits, fish and shellfish can also become contaminated by accumulating metals from the very soil and water it grows from.
Phosphate
Nitrate
Nitrate (NO3) is a naturally occurring form of nitrogen found in soil. Nitrogen is essential to all life. Most crop plants require large quantities to sustain high yields.
The formation of nitrates is an integral part of the nitrogen cycle in our environment. In moderate amounts, nitrate is a harmless constituent of food and water. Plants use nitrates from the soil to satisfy nutrient requirements and may accumulate nitrate in their leaves and stems. Due to its high mobility, nitrate also can leach into groundwater. If people or animals drink water high in nitrate, it may cause methemoglobinemia, an illness found especially in infants.
Nitrates form when microorganisms break down fertilizers, decaying plants, manures or other organic residues. Usually plants take up these nitrates, but sometimes rain or irrigation water can leach them into groundwater. Although nitrate occurs naturally in some groundwater, in most cases higher levels are thought to result from human activities. Common sources of nitrate include:
fertilizers and manure,
animal feedlots,
municipal wastewater and sludge,
septic systems, and
N-fixation from atmosphere by legumes, bacteria and lightning.
Health Effect of Nitrates
People
High nitrate levels in water can cause methemoglobinemia or blue baby syndrome, a condition found especially in infants under six months. The stomach acid of an infant is not as strong as in older children and adults. This causes an increase in bacteria that can readily convert nitrate to nitrite (NO2). Do not let infants drink water that exceeds 10 mg/l NO3-N. This includes formula preparation.
Nitrite is absorbed in the blood, and hemoglobin (the oxygen-carrying component of blood) is converted to methemoglobin. Methemoglobin does not carry oxygen efficiently. This results in a reduced oxygen supply to vital tissues such as the brain. Methemoglobin in infant blood cannot change back to hemoglobin, which normally occurs in adults. Severe methemoglobinemia can result in brain damage and death.
Pregnant women, adults with reduced stomach acidity, and people deficient in the enzyme that changes methemoglobin back to normal hemoglobin are all susceptible to nitrite-induced methemoglobinemia. The most obvious symptom of methemoglobinemia is a bluish color of the skin, particularly around the eyes and mouth. Other symptoms include headache, dizziness, weakness or difficulty in breathing. Take babies with the above symptoms to the hospital emergency room immediately. If recognized in time, methemoglobinemia is treated easily with an injection of methylene blue.
Healthy adults can consume fairly large amounts of nitrate with few known health effects. In fact, most of the nitrate we consume is from our diets, particularly from raw or cooked vegetables. This nitrate is readily absorbed and excreted in the urine. However, prolonged intake of high levels of nitrate are linked to gastric problems due to the formations of nitrosamines. N-nitrosamine compounds have been shown to cause cancer in test animals. Studies of people exposed to high levels of nitrate or nitrite have not provided convincing evidence of an increased risk of cancer.
Dissolved ammonia
Surface water may contain up to 12mg|l dissolved ammonia. The presence of ammonia in drinking wtare is caused by the disinfection with chloramines. An increased level of dissolved ammonia is an essential indicator of faecal pollution. Taste and odour problems as well as decreased disinffection efficiency are to be expected if ever the drinking water contains more than 0.2g of dissolved ammonia in one litre of water.
Cement motars used for the coating of inside surface of wtare pipes may relase considerable amounts of ammonia in drinking H2O and compromise disinfection with chlorine.
