Purifying water

Water gets polluted when it is piped to users due to various factors. Further purification is necessary.

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.

Boiling and Filtering

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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.

Chemical Disinfection

This is useful when purifying stored water as in sumps, overhead tanks or well water.

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.

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.

Chlorine Solution

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.

Chlorine tablets

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.

Filters

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.

U-V Filters

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.

(Source: Webhealthcenter.com)