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. So, water treatment is a multi-pronged process, and the contaminant challenge has a big say in selecting appropriate technology.

Treatment processes either remove contaminants or destroy them. Removal technologies include ion exchange, adsorption and filteration (see flow diagram: Water treatment). Then there are technologies that decompose chemicals and pesticides by oxidation or hydrolysis. Chlorination, for example, is also known to oxidize and remove many pollutants. Disinfection is a similar technology.

Let us now see how most common filters work:

Activated carbon filter
These filters follow a two-pronged approach.Firstly, some contaminants are blocked by pores