New Delhi, Sept. 5 -- The first thing many people do after checking their home's water is reach for an RO purifier. The TDS is high, so it must need RO. The water tastes strange, so RO should fix it. The house uses borewell water, so an RO purifier seems like the obvious choice.

But these conclusions can be too quick.

Water quality is not determined by a single number, a particular taste or even the source of the water. A TDS meter can tell you something about dissolved substances, but it cannot tell you everything about the water. Similarly, borewell water isn't automatically the same from one locality to another.

That matters when you are about to spend thousands of rupees on a water purifier.

The better approach is to identify the ...