A water purifier has to deal with physical, chemical and biological adulterants including dissolved solids, heavy metals and pesticides. Besides, all contaminants have different characteristics like molecular weight and size, water solubility, volatility and ability to react with oxygen.

The system wastes water, and is expensive

According to industry estimates, 5.2 million households use water purifiers of which about 42 per cent (or 2.1 million households) employs RO. Assuming every household has 5 members;

How does one select a water filter?

Step 1: Understand raw water quality. Find out the contaminants in water, its hardness and its total dissolved solid contents. Also find out if the water has heavy metals, pesticides or any other chemical

A consumer looking for a water purifier is most likely to be confronted with a fusillade of quality claims. K J Nath, president, Institution of Public Health Engineers in Kolkata is not sure about their veracity. "A lot of the tall claims by private players cannot be substantiated scientifically,' he says.

The BIS drinking water specification (IS 10500:1991), which is a voluntary standard, was drawn up in 1983. It was last revised 17 years ago. A revision initiated in 2003, is still in its draft stage.

We asked a few manufacturers about the standards they adhere to. Here is what they said

Philips Electronics India: Gold seal Class A certified by the US-based Water Quality Association, certified by KIWA Water Research of the Netherlands and BIS certification for UV filters

Industry sources exude confidence about the water purifier segment. Manufacturers peg their hopes on the increasing purchasing power of the middle class in cities, small towns and the suburbs.

This article describes the Reverse Osmosis technology and its cost economics to convert the brackish ground water and tap water of poor quality to potable water.