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 Water & Hydration

June 2010
Purifying Water
Dr Sreedevi Yadavalli
Water purification is an absolute necessity now, considering the threat of water-borne infections that we face with regard to our drinking water. Here we give you a lowdown on the filtering options available.

Impurities in potable water are mainly of two kinds: dissolved and suspended. Dissolved impurities mainly consist of salts and minerals. While some minerals are necessary for our consumption, others like arsenic, lead, etc., are harmful. Suspended impurities consist of particulate matter like sand, algae, virus and bacteria, which can cause diseases like diarrhoea, gastroenteritis, etc. The following are the major methods of purification commonly employed:

Filtration is one of the oldest forms of water purification. Water is passed through a candle type of filter, from one chamber to another, so that all larger suspended impurities are removed. Smaller particles like bacteria and virus remain.

Ultra Filtration uses a polymer film in place of the regular granular candle. The size of the film used determines the size of particles and organisms filtered out.

Boiling is also a very old and popular method of treating water, which neutralizes bacteria and virus quite effectively, though the rest of the suspended and dissolved impurities are not addressed.

Chlorination is what municipal authorities employ to destroy micro-organisms. But excessive addition of the chlorine tablets may prove harmful. Besides, the remaining insoluble or dissolved impurities remain unaddressed.

Activated Carbon filtration is most effective in removing contaminants like organic substances that are often responsible for taste, odour and colour problems.

UV Treatment has been a popularly employed in urban homes over the last two decades. When combined with some preliminary filter treatments, it addresses many of the impurities found in tap water, though it does not address dissolved impurities. Reverse Osmosis (RO) literally reverses osmosis through a semi permeable membrane to ensure that water flows from the side with dissolved impurities to the side with no impurities, under artificially applied pressure. When combined with other preliminary filtration methods, this filters out water of most impurities - dissolved or suspended.

Mineral RO System has water being subjected to UV filtration after the preliminary round. It is then treated by the RO method. However, some of the water from the UV stage is tapped and added to the finally filtered water after the RO treatment, so as to add the benefits of lost minerals.

Testing your tap water

When investing in a water purification system for your home, you will need to assess your tap water for Total Dissolved Solids (TDS), which the brand salesman will help you with. TDS of about 50 ppm (parts per million) is recommended, but up to 500 ppm may be acceptable. 750-1000 ppm means your water is contaminated, and above 1500 means you’re drinking liquid manure! You must remember that a lower TDS is no guarantee that your water is free of dissolved heavy metal, so the salesman may recommend electrolysis of your water sample to give you an idea of the metals dissolved in it, based on the colours of the precipitate.

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