Seven questions to ask before you buy any purifier

Purifiers are sold on a demonstration and a number. Both are easy to stage. These are the questions that are harder to stage, and they work on any brand.

1. What comes out, not just what goes in

Ask for the permeate composition — pH, hardness, nitrate, the lot. A TDS reduction figure alone tells you how much was removed, not what remains.

2. Across what range of feed water?

A result from one convenient sample means little. Indian supply varies by city, season and source, so ask what happens at 250 mg/L TDS and again at 1,500.

3. What is the pH of the output?

BIS specifies 6.5–8.5. Units that strip water and then correct it with an alkaline stage can overshoot — the competitor RO in the IAPMO series came out at 9.7, outside that range.

4. How much water reaches the glass?

Recovery, as a percentage. Anything around 40–50% means roughly three glasses discarded for every one you drink.

5. What does it cost to keep, not to buy?

Filters, membranes and servicing over five years. Ask for the total, not the sticker.

6. Who tested it, and can you see the report?

Independent certification with a report number you can check. "Lab tested" without a reference is not a claim, it is a phrase.

7. What happens when my water changes?

Sources get switched, tankers arrive, monsoon dilutes and summer concentrates. Ask how the unit behaves when that happens.