The right water purifier depends on one number and one question: the TDS of the water coming into your kitchen, and whether that water is from a borewell, a tanker or a municipal line. If your tap water has low TDS and comes from a treated municipal supply, a UV or UF purifier is usually enough and an RO wastes water for little gain. If it is borewell or tanker water, or TDS is high, you need RO, ideally paired with UV or UF. Everything else — copper, alkaline, "mineraliser", smart apps — comes after that decision.
This guide explains what RO, UV and UF actually do, how to read a TDS number, which extras are worth paying for, and what to check on a listing before you order.
Step 1: Test your water before you shop
TDS (total dissolved solids) is the amount of salts and minerals dissolved in water, measured in mg/L or ppm, which are the same unit. India's drinking water standard, IS 10500, sets an acceptable limit of 500 mg/L and allows up to 2,000 mg/L only where no better source is available, as summarised by India Water Portal.
A basic digital TDS meter is the easiest way to check at home. Eureka Forbes' TDS guide says to keep the probe submerged without touching the container walls and wait for the reading to settle. Test the tap that will feed the purifier, not a bottle or an existing filter's output, and test again in a different season if your supply changes (many homes switch between municipal water and a tanker in summer).
Two important limits of a TDS meter:
- TDS is not a safety score. WHO has proposed no health-based guideline for TDS; high TDS mainly affects taste and causes scaling. Low TDS does not mean the water is free of bacteria.
- It cannot see specific contaminants. Arsenic, fluoride and nitrates can be harmful even in small amounts and have their own limits, as India Water Portal notes. If your area has a known problem, or you rely on a borewell, a lab test of the water is worth more than any purifier feature list.
Step 2: Understand what RO, UV and UF actually do
| Technology | What it does | What it does not do | Needs electricity |
|---|---|---|---|
| RO (reverse osmosis) | Pushes water through a membrane that removes most dissolved salts and metals; reduces TDS | Removes useful minerals too, and rejects part of the input water as waste | Yes, with a pump |
| UV (ultraviolet) | Kills bacteria and viruses | Does not reduce TDS or remove dissolved salts, metals or dead microbes | Yes |
| UF (ultrafiltration) | A fine hollow membrane filters out suspended particles and microbes | Does not reduce TDS or remove dissolved salts and metals | No |
These descriptions follow A.O. Smith's explainer on RO, UV and UF, which also puts RO's TDS reduction at around 90%. The practical takeaway: UV and UF deal with germs, RO deals with what is dissolved in the water. Most purifiers sold in India combine them as "RO + UV + UF" so one unit covers both.
Step 3: Match the technology to your water source
Eureka Forbes, which makes Aquaguard, gives a sensible rule of thumb in its borewell vs municipal guide: borewell water often exceeds the 500 mg/L limit, so RO is the usual choice there, while municipal water is generally lower in TDS, so UV or UF alone is often enough. For a mixed or changing supply, it recommends RO + UV + UF.
Put together with the IS 10500 limit, a practical way to decide:
- Municipal water, TDS comfortably under 500 mg/L, taste is fine: UV, UF or UV + UF. Lower running cost, no wasted water. Check the model's stated maximum input TDS — Eureka Forbes lists one of its UV models as suitable up to 200 mg/L, for example.
- Borewell or tanker water, or TDS above 500 mg/L: RO + UV (or RO + UV + UF). Check the maximum input TDS the purifier is rated for and make sure your reading is well inside it.
- Supply switches between sources, or you are not sure: RO + UV + UF covers both cases.
- Known arsenic, fluoride or other contamination: get a water test and choose a purifier whose maker specifically claims to handle that contaminant — do not rely on a generic "RO" label.
This also matters legally and environmentally. In 2019 the National Green Tribunal asked the government to ban RO where TDS is below 500 mg/L and to require RO units to recover at least 60% of the input water, as Down To Earth reported. The Supreme Court stayed a later NGT direction on the ban in March 2022, according to Verdictum, so RO is still freely sold. But the reasoning holds: if your water is already low in TDS, RO adds cost and waste without much benefit.
Step 4: Check water recovery if you buy RO
Every RO purifier sends part of the input water down the drain as "reject" water. The Down To Earth report notes that an older standard allowed recovery as low as 20%, meaning four litres wasted for every litre you drink, which is why the NGT pushed for 60% and eventually 75%.
Brands now advertise recovery, but treat these as the maker's own claims. Native by Urban Company, for instance, states 48.7% RO recovery for its M2 Pro against 25% for a "standard RO", based on its own tests. When comparing, look for a stated recovery percentage on the brand's page or manual; if none is given, assume it is not a strength.
The reject water is not useless. The NGT report suggests reject water with TDS below 2,100 mg/L can be used for mopping, washing vehicles, flushing and gardening. A bucket under the drain pipe is the cheapest water saving you can make.
Step 5: Decide which extras are worth it
TDS controller (MTDS). Many RO purifiers, such as the KENT ACE Copper - B, list "TDS Control". It works by sending a small share of input water around the RO membrane, through UV or UF only, and blending it back to raise TDS and improve taste. Urban Company's article on TDS controllers argues this can let metals in the source water through, because UV and UF do not remove them. Note that Urban Company sells purifiers without this feature, so it has a commercial angle — but the mechanism it describes is accurate. Our view: a TDS controller is fine for municipal water that is mainly high in harmless salts; if your water may carry heavy metals, keep it at its lowest setting or choose a model that adds minerals back after RO instead.
Mineraliser, copper and alkaline stages. These add minerals or copper to RO water after purification, mainly for taste. The Aquaguard Sure Delight RO+MC is an example of an RO + minerals design. They are reasonable if you are buying RO anyway; they are not a reason to buy RO when you do not need it.
Storage tank size. Most purifiers on our deals page store 6–8 litres; a few go up to 15–18 litres. A bigger tank helps if you have long power cuts, since RO and UV need electricity to purify.
Smart features and filter-life alerts. Useful if they tell you when to change filters; less useful if they only add an app.
Step 6: Count the cost of owning it, not just buying it
The purchase price is only part of what you pay. Filters and membranes wear out, and RO purifiers need more servicing than UV or UF units. Before ordering, check on the brand's site:
- Filter replacement cost and interval, or the price of the annual maintenance plan.
- Warranty terms — whether filters and the membrane are covered, or only the electrical parts.
- Service coverage in your pin code. Installation and filter changes need a technician, so a brand with good service in your city matters more than an extra stage.
- "No service for X years" claims. Some models, such as Native's M1 and M2 Pro, are sold on long filter life. Read the conditions behind them, such as the maximum input TDS the model is rated for.
Step 7: Check the listing before you order
Use our water purifier deals page to see current offers, and check each product's price record on the price tracker so you know whether a sale price is genuinely lower. On the listing itself, confirm:
- The technology combination (RO, UV, UF) matches your water from Step 3.
- The maximum input TDS covers your reading with room to spare.
- Storage capacity — listings can differ from the brand's page, so check both. Our current listing for the Native M2 Pro, for example, says 7 L while Native's own page says 8 L.
- Whether free installation is included and who does it (the brand or the seller).
- Wall-mount or countertop, and whether you have a power point and drain near the sink.
For more home appliance advice, browse our buying guides.
Frequently asked questions
Do I need an RO purifier for municipal water?
Usually not, if your tap water's TDS is well below 500 mg/L and it comes from a treated municipal supply. A UV or UF purifier handles germs without wasting water. Choose RO if TDS is high, the supply mixes in borewell or tanker water, or the taste is poor.
What TDS level is good for drinking water?
India's IS 10500 standard sets 500 mg/L as the acceptable limit. Eureka Forbes describes 150–300 ppm as generally ideal and notes that water below 50 ppm may lack minerals such as calcium and magnesium. Remember that TDS does not measure bacteria, arsenic or fluoride.
Is a TDS controller safe?
It mixes a small amount of water that has only passed UV or UF back into RO water. That is fine for water that is mainly high in harmless salts, but if your source may contain heavy metals, those can pass through. Use the lowest setting or prefer a post-RO mineraliser in that case.
How much water does an RO purifier waste?
It depends on the model's recovery rate. Older RO units could recover as little as 20% of the input water. The NGT has pushed for at least 60%. Check the stated recovery on the brand's page and reuse reject water for mopping or gardening.
Can I use a UF purifier without electricity?
Yes. UF works on tap pressure and needs no power, but it does not reduce TDS, so it only suits water that is already low in dissolved salts.
