The water purifier aisle is full of acronyms, but the decision mostly comes down to one number: how much dissolved material is in your water. Find that out first, and the right technology follows.
Step 1: Test your water
- TDS (total dissolved solids): a cheap handheld TDS meter gives a reading in seconds. Test the water at the tap you will connect the purifier to.
- For borewell water, or if you are in an area known for fluoride, arsenic or nitrate contamination, get a lab test. A TDS meter only measures the total amount of dissolved material, not which contaminants are present. Many state water departments and private labs offer these tests.
The BIS drinking water standard (IS 10500) gives an acceptable TDS limit of 500 mg/L and a permissible limit of 2,000 mg/L only where no alternative source exists.
Step 2: Understand what each technology does
| Technology | Removes | Does not remove | Needs power | Wastes water |
|---|---|---|---|---|
| RO (reverse osmosis) | Dissolved salts, hardness, heavy metals, fluoride, arsenic, most microbes | — (but it also removes useful minerals) | Yes | Yes |
| UV (ultraviolet) | Kills or inactivates bacteria and viruses | Dissolved salts, chemicals, mud | Yes | No |
| UF (ultrafiltration) | Bacteria, cysts, suspended particles, turbidity | Dissolved salts and chemicals. Removal of smaller viruses varies | No | No |
That’s why purifiers combine stages, such as RO + UV + UF: each stage covers what the others miss.
Step 3: Match the purifier to your water
- Municipal water, TDS under about 300 mg/L: UV + UF. You get microbial safety and keep the natural minerals, with no wasted water.
- TDS of about 300–500 mg/L: either works. Choose RO with a TDS controller if the water tastes salty or leaves heavy scaling.
- TDS above 500 mg/L, borewell or tanker water: RO + UV, ideally with a TDS controller or mineraliser.
- Low TDS, unreliable electricity: a gravity-based UF purifier with a storage tank.
Step 4: Compare running costs, not just the price
The purchase price is only part of what you’ll spend. Over three to five years:
- Filter and membrane replacements usually add up to more than the purifier cost.
- AMC (annual maintenance contract) plans bundle filters and service visits. Compare the AMC price with the cost of buying filters separately.
- Water recovery: a water-saving RO wastes much less water. That matters if you pay for water or rely on tankers.
- Service network: as with any appliance, recent reviews from your city matter more than national ratings.
Other features worth checking
- Storage tank: 6–10 litres is typical. Bigger tanks help during power cuts. Food-grade plastic or a stainless-steel tank is preferable.
- Filter-change indicator and app alerts: helpful, because most people forget to change filters.
- Installation: wall-mounted or under-sink, and whether installation and the first-year service are free.
- Hot water or alkaline features: mostly marketing. Don’t pay a lot extra for them.
Next: we are testing popular RO + UV and UV + UF models. That roundup is coming soon.
Frequently asked questions
What TDS level needs an RO purifier?
The Bureau of Indian Standards (IS 10500) sets an acceptable limit of 500 mg/L for total dissolved solids in drinking water, and allows up to 2,000 mg/L only where no other source is available. If your water is above about 500 mg/L, or a lab test shows fluoride, arsenic or nitrates, you need RO. If it is well below that and comes from a treated municipal supply, UV + UF is usually enough.
Does RO remove good minerals from water?
Yes. RO removes most dissolved minerals, including calcium and magnesium. Many RO purifiers add a mineraliser or a TDS controller that blends some filtered water back in to raise the TDS. Most people get far more of these minerals from food than from water.
How often should water purifier filters be changed?
Usually every 6 to 12 months for the sediment and carbon filters, and every 1 to 3 years for the RO membrane. Change them sooner if your water is very hard or high in TDS. Follow the manufacturer's indicator or schedule.
How much water does an RO purifier waste?
Older RO units could reject 3 litres or more for every litre purified. Newer 'water-saving' models recover a much larger share. Check the recovery figure the brand quotes, and reuse the reject water for mopping or plants.
