1.What is potable water and what are its sources?
Safe and wholesome water is defined as water,
which is free from disease carrying micro organisms ,
Free from dangerous chemical substances
In urban areas and big towns, the corporation or municipality undertakes the treatment of water from surface water sources and supplies it to users.
- What are the pollutants common in water?
Naturally found water is not pure H2O. It contains natural impurities of various kinds – both dissolved and suspended impurities. These are the impurities derived from atmosphere, catchment area and soil. They can be dissolved substances – hydrogen sulphide, oxygen, ammonia, sodium or suspended impurities such as clay, silt, sand, mud and microscopic plants and animals.
The more hazardous water pollution is caused by human activity like urbanization and industrialization. Sources of pollution resulting from these are:
- Industrial and trade waste which contain toxic agents ranging from metallic salts to complex synthetic organic chemicals.
- Sewage which contains decomposable organic matter and disease carrying microbes.
- Agricultural pollutants like fertilizers and pesticides such as DDT, Aldrin, dioxin.
- Nuclear wastes.
- What are the hazards of using polluted water?
These can be classified under two broad groups as biological and chemical.
Biological Hazards are caused by the presence of an infective agent or an aquatic host.
The presence of virus, bacteria, worms etc. causes:
- Gastric Problems
- Dysentery (both amoebic and bacterial)
- Round worm infestation
- Guinea worm infestation
The pollutants include various chemicals, such as detergents, solvents, cyanides, heavy metals, mineral and organic acids, nitrogenous substances, bleaching agents, dyes, pigments, sulphides, ammonia, toxic and biocidal organic compounds of great variety. Chemical pollutants may affect our health not only directly but also indirectly by accumulating in aquatic life such as fish that are consumed by humans.
Some of the diseases that can be spread by chemical pollutants are:
- Skin infections
- Intestinal disorders (by Polychlorinated biphenyls)
- Disorders of liver, bone and circulatory system, birth anomalies (by Vinyl chloride)
- Anaemia, bone marrow damage, leukaemia (by Benzene)
- Damage to central nervous system (by Phthalates)
- Carcinogenic problems (by Nitrosamine)
Though pollution seems to be an inevitable consequence of modern industrial technology, the challenge is to determine the level of pollution that permits economic and social development without causing hazards to health.
4. What are the criteria for water quality?
Drinking water should be:
- Clear, colourless, odourless and tasteless.
- Free of chemical substances such as chlorides, hardness, free and saline ammonia, albuminoidal ammonia, nitrites and nitrates, oxygen, and dissolved oxygen. Toxic substances such as arsenic, cadmium, cyanide, lead, mercury, and selenium etc. indicate chemical contamination of water.
- Free of bacteria such as E. coli, and fecal streptococcus, clostridium perfringens, which indicate fecal pollution.
- How can we purify polluted water?
Purification of water is of great importance. Urban Water supply is purified in three stages: storage, filtration and chlorination. Despite this process, water gets polluted when it is piped to users due to various factors specific to India. Therefore, further purification at home becomes necessary.
1. Boiling and Filtering
This is an easy, time tested and a satisfactory method of purification in households. Water must be brought to a rolling boil for five to ten minutes. It kills bacteria, spores, ova, cysts and sterilizes water. It also removes temporary hardness by driving off carbon di-oxide and precipitating calcium carbonate.
There are some disadvantages in the process. The taste is altered. The precipitates have to be filtered out. It gives no residual protection, meaning, after boiling, if the water is transferred to another container, which is infected, the effects of boiling will be lost.
2. Chemical Disinfection
This is useful when purifying stored water as in sumps, overhead tanks or well water.
3. Bleaching Powder
This is chlorinated lime. It is a white powder with a pungent smell.
2.3 grams of bleaching powder is required to disinfect one cubic meter of water.
1 L ≡ 0.001 m3 ≡ 1000 cm3, and
1 m3 is exactly 1000 L.
(i.e. a cubic metre, which is the SI unit for volume) From 1901 to 1964, the litrewas defined as the volume of one kilogram of pure water at maximum density and standard pressure).
(Average of bleaching powder is 250 grams for 1 lakhs Lit water)
Bleaching powder is an unstable compound. When it is exposed to air, light or moisture, it quickly loses its chlorine content and becomes ineffective. Highly polluted and turbid water cannot be purified by this method.
If 4 kg of bleaching powder with 25% available chlorine is mixed with 20 litres of water it will give a 5% chlorine solution.
Like bleaching powder this is also unstable and has to be stored in a cool, dark place.
These are available in the market under various trade names, such as halazone tablets. These are expensive but effective for small quantities of water.
Smarter chlorine tablets have been introduced recently. These are about fifteen to twenty times as powerful as the halogen tablets.
One pill of 0.5gms is enough to disinfect 20 litres of water.
Potassium Permanganate and Iodine are disinfecting agents too but high costs and side effects are their drawbacks.
Porcelain Candle filters
Water can be filtered with ceramic filters. The main part of a filter is, a candle made from porcelain or infusorial earth. The surface is coated with silver catalyst so that the bacteria coming into contact with it is killed. This method removes the bacteria found commonly in drinking water but is not effective with virus that can slip through the filter.
The candle has to be washed thoroughly once a week as it gets clogged with coagulated bacteria and other impurities.
These are gaining wide acceptance in urban households. A U-V filter apparatus usually consists of a preliminary filter, which strains out physical impurities. An activated carbon cartridge rids the water of organic impurities like colour, odour, free chlorine etc.
An ultraviolet beam eliminates bacteria and viruses.
As this is done on the line, as the water runs out of the tap, there is less risk of recontamination.
The activated carbon should be changed at intervals depending on the usage and quality of water supply.
WATER BLEACHING RATIO
10 GALLON – 1 TEASPOONE
1 Gallon (Liquid) = 3.785411784 Liters
1 cubic meter of water (m3 – cu m) = 1,000.00 liters of water (l)
fitkari is called alum in English.
Fitkari will only help settle down the suspended particles in the water, it will not “purify” it. Only the water so treated will look clean.
About 1 gm of alum powder for every liter of muddy water
The common formula of fitkari is
Double sulfates with the general formula A2SO4·B2(SO4)3·24H2O, are known where A is a monovalent cation such as sodium, potassium, rubidium, cesium, or thallium(I), or a compound cation such as ammonium (NH4+), methylammonium (CH3NH3+), hydroxylammonium (HONH3+) or hydrazinium (N2H5+), B is a trivalent metal ion, such as aluminium, chromium, titanium, manganese, vanadium, iron (III), cobalt(III), gallium, molybdenum, indium, ruthenium, rhodium, or iridium. Alums crystallize in one of three different crystal structures. These classes are called α-, β- and γ-alums They are soluble in water; have an astringent, acid, and sweetish taste; react acid to litmus; and crystallize in regular octahedra. When heated they liquefy; and if the heating is continued, the water of crystallization is driven off, the salt froths and swells, and at last an amorphous powder remains.