How to Choose a Water Purifier in India: RO vs UV vs UF, Sizing, AMC Cost and a Buyer's Checklist

Buying a water purifier in India is not really a shopping problem — it is a water problem wearing a shopping disguise. Two homes on the same street can need completely different machines because their water is different. This guide is the buying decision: how to read your own water, pick the right technology, and then judge storage, running cost, standards and service before you pay. For how each technology actually works, we link the water treatment guide — this page keeps to the choice.

Start where every honest purchase starts: with the plumbing buying guide mindset — match the product to the need, not to the salesperson's margin.

Step 1: Test your water — it decides everything

The single most expensive mistake is buying a purifier type before you know your water. A ₹18,000 RO machine on clean municipal water wastes litres and strips minerals; a ₹6,000 gravity filter on high-TDS borewell water leaves the salt exactly where it was.

Two numbers settle the technology:

• TDS (total dissolved solids) — the dissolved salts a cheap TDS meter reads in mg/L. It decides whether you need RO, because RO is the only home technology that removes dissolved solids.
• Microbial safety — whether bacteria, viruses or cysts are present. It decides whether you need UV or a membrane fine enough to block them.

Do not guess these. Test your water — a TDS meter plus, ideally, a lab report for hardness, nitrate, fluoride, iron and bacteria. IS 10500, the Indian drinking-water standard, sets an acceptable TDS of 500 mg/L (permissible 2000 mg/L where no alternative source exists). That 500 number is your first fork in the road.

Step 2: Match your water to the right technology

Each technology has its own treatment guide explaining the physics; here is only what you need to make the buying call.

The combinations exist for a reason: real water often has both problems. High-TDS and microbially unsafe borewell water wants RO + UV. High TDS with turbidity wants RO + UF. Buy the combo only if the test justifies each stage — every extra stage is another cartridge to replace later, and every unnecessary stage is money you pay again every service visit.

A word on marketing acronyms: shops love to stack letters — "RO+UV+UF+TDS+Alkaline+Copper" — to justify a higher price. Each of those does something, but only some of it is something your water needs. The test tells you which letters earn their place. Alkaline and copper add-ons are wellness features, not safety features; treat them as optional, not as reasons to move up a price bracket.

The one rule to tattoo on your wallet: do not buy RO for low-TDS water. Below ~200 mg/L, RO throws away 2-3 litres of water per litre purified and removes calcium and magnesium your body wants. If a machine you like is RO-based, insist on a TDS controller / mineraliser that blends minerals back and lets you set output TDS — and question whether you needed RO at all.

Step 3: Now the buying decisions

Technology chosen, the money decisions begin. These separate a good buy from an expensive regret.

Storage capacity

RO and UV purifiers with a pump store purified water in a tank so you are not waiting at the tap. For a family of 4-5, a 7-9 litre tank is the sweet spot. Too small and it runs dry at dinner during a power cut; too large and water sits stagnant and stale. If your area has frequent outages, a larger stored volume is genuine insurance, since a pumped purifier will not make water without electricity. Gravity purifiers are pure storage and need no power — pick them by how many litres you draw between refills.

Purification rate

Measured in litres per hour (LPH). A domestic RO typically does 12-20 LPH. If several people fill bottles at once, or you cook heavily, a higher rate matters more than a bigger tank.

AMC and filter-replacement cost — the real long-term spend

This is where buyers get ambushed. The sticker price is a fraction of lifetime cost. Filters and membranes are consumables: sediment and carbon pre-filters every 6-12 months, the RO membrane every 2-3 years, the UV lamp roughly yearly. An Annual Maintenance Contract (AMC) bundles these.

• Ask for the AMC price in writing and what it covers — labour only, or parts too.
• Ask the out-of-warranty cost of each cartridge and the membrane separately, so you can compare brands honestly.
• A cheaper machine with a costly, proprietary-cartridge AMC can lose to a dearer machine with standard filters within two years.

For a full breakdown and indicative numbers, see the water treatment cost guide — prices here are indicative only, e.g. an AMC in the ₹2,500-₹5,000/year range for a typical RO+UV unit.

BIS / ISI mark and standards

Insist on genuine certification. Look for the ISI mark and, for the UV disinfection performance, conformance to relevant BIS standards for water purifiers. The drinking-water quality target itself is IS 10500. Certification is your defence against substandard membranes and counterfeit lamps that look identical but fail early.

Warranty and service network

• Warranty: 1 year is common; some brands offer longer on the RO membrane. Read what is excluded (consumables usually are).
• Service network: a purifier is a subscription to service, not a one-time purchase. Before buying, confirm the brand has a technician who actually services your pincode and a working complaint channel. A great machine with no local service is a bad buy.
• Branded vs local/unbranded: unbranded assemblers undercut on price but leave you with no warranty, no ISI, and orphan cartridges. For a health-critical appliance, buy branded with verifiable service.

Good / better / best at a glance

"Best" here means best-fitted, not most expensive: on low-TDS water the RO tier is the wrong choice, not the premium one.

A note on smart purifiers

Some purifiers now add app connectivity — filter-life alerts, usage tracking, auto service booking. Genuinely useful for remembering cartridge changes, but do not let a screen substitute for the fundamentals above: water test, right technology, real service network. Treat connectivity as a bonus, and if you are wiring a connected home, plan it alongside your smart home systems rather than as an afterthought.

Buyer's checklist

• Test first. TDS meter plus a lab report — the test picks the technology.
• Match, don't upsell. RO for high TDS, UV for microbial risk on low-TDS water, UF/gravity for clean-but-turbid.
• Never RO low-TDS water — and demand a mineraliser/TDS controller if you do go RO.
• Cost the consumables, not just the sticker: AMC, cartridges and membrane over 3 years.
• Insist on ISI; target IS 10500 water quality; avoid unbranded no-warranty units.
• Confirm local service for your pincode before you pay.

References

• IS 10500 — Indian Standard for Drinking Water Specification (BIS).
• ISI mark — Bureau of Indian Standards (BIS) product certification.