What is the best method of water purification?
P.Ramesh Kumar, Sathyavedu ANSWER: Boiling is an excellent method of purifying water for household purposes. To be effective the water must be brought to a `rolling boil’ for 15 minutes to kill all pathogens of bacteria, viruses, spores, cysts, ova to yield sterilised water. This process also removes temporary hardness, by driving off CO{-2} and precipitating calcium carbonate. It offers no residual protection against subsequent microbial contamination and to avoid this the water should be stored in the same vessel. Chlorination of water is being widely practised for urban supply. The principle in chlorination is to ensure free residual chlorine of 0.5 mg per litre at the end of one hour’s contact. Chlorine tablets are quite good for disinfecting small quantities of water. A single tablet of 0.5 gm is sufficient to disinfect 20 litres of water. Two drops of 2 per cent ethanol of iodine will suffice for one litre of clear water to disinfect it. Its physiological activity over thyroid gl
