Purification of Water.

If you want to install water purifier, first of all, check the TDS (Total Dissolved Solids) level of your water.
If TDS level is high or very high, then simple water purifier (with UV purification) will not be of much use except it removes bacteria, viruses and cysts. It does not remove TDS from the water.

For high TDS level, install purifier with RO technology.

Reverse Osmosis (RO) is an advanced water purification technology.

Reverse Osmosis (R.O) is the process by which water molecules are forced, by water pressure, through a semi permeable membrane. Most of the impurities and other contaminants are rinsed to the drain while the refined water is routed to a special holding tank.

The special features of RO process is its ability to remove not only the suspended impurities but also dissolved impurities and salt which are harmful and spoil the taste of water. In addition, it also removes bacteria and virus better than the conventional purifiers.

The pore size of RO membrane is less 0.0001 micron (which is 50,000 times less than the diameter of our hair).

http://www.eurekaforbes.com/ website may be useful.

Update 1 : [06.06.2010]

Now companies have started giving some more informations on water purifiers.

The following ad has written-

" Issued in public interet: RO water purifiers waste upto 80% of water. It should only be used in areas where TDS levels are over 500 mg/l"