💧 Water technology · Head to head

RO vs UV Water Purifier: Which One Do You Actually Need?

8 min read · Updated 1 August 2026

RO (Reverse Osmosis)

Pushes water through a semi-permeable membrane under pressure, removing dissolved salts, heavy metals and most of what makes water taste bad.

UV (Ultraviolet)

Passes water past a UV-C lamp that inactivates bacteria, viruses and cysts, leaving everything dissolved in the water exactly as it was.

Side by side

RO (Reverse Osmosis) compared with UV (Ultraviolet)
	RO	UV
Removes dissolved solids (TDS)	Yes, 90-98%	No
Removes heavy metals, arsenic, fluoride	Yes	No
Kills bacteria and viruses	Yes — physically excluded by the membrane	Yes — inactivated by UV-C
Removes dead microbes from the water	Yes	No — they stay in the water, inactive
Handles turbid or sediment-heavy water	Yes, with pre-filtration	No — UV needs clear water to work at all
Needs electricity	Yes	Yes
Needs water pressure	Yes, or a booster pump	No
Water wasted	1-3 L per L purified	None
Retains natural minerals	No — needs a TDS controller or mineraliser	Yes
Typical purchase price	₹9,000-25,000	₹5,000-12,000
Typical annual running cost	₹3,000-5,000	₹1,200-2,000
Suitable input TDS	Up to 2,000 ppm (3,000 ppm on brackish-rated units)	Below ~200 ppm

RO (Reverse Osmosis) compared with UV (Ultraviolet)

Choose RO (Reverse Osmosis) if…

Your measured TDS is above 300 ppm.
Your supply is borewell, tanker-fed, or you genuinely do not know where it comes from.
Water tastes salty, bitter or metallic — all dissolved-solid problems UV cannot fix.
Your area has documented arsenic, fluoride, nitrate or heavy-metal issues.
Supply quality swings between seasons, so you need to design for the worst reading rather than the average.

Choose UV (Ultraviolet) if…

Your measured TDS is consistently under 200 ppm and the supply is treated municipal water.
Water tastes fine and the only worry is microbiological safety.
You want to keep calcium and magnesium in the water rather than strip and re-dose them.
You care about not wasting 2 litres to drink 1 — a real consideration in a water-stressed city.
You want the lowest running cost available from a powered purifier.

The difference in one sentence

RO removes what is dissolved in water. UV kills what is alive in it. They are not competing solutions to the same problem — they are solutions to two different problems, and which one you need depends entirely on which problem your supply actually has.

This gets muddled at the point of sale because almost every purifier over ₹10,000 in India bundles both, and the salesperson has no incentive to tell you that one of the two is doing nothing useful for your water. On genuinely soft, chlorinated municipal supply, an RO membrane is solving a problem you do not have, at a cost of roughly ₹2,500 a year and two wasted litres for every litre you drink.

What each one physically does

An RO membrane has pores in the region of 0.0001 microns. Water is forced through under pressure; dissolved sodium, calcium, magnesium, nitrate, arsenic, fluoride and lead ions are too large to follow, and leave down the reject line. It is a physical separation, so it also excludes bacteria, viruses and cysts as a side effect.

A UV chamber does no filtering at all. Water flows past a UV-C lamp — usually 254 nm — which scrambles the DNA of any microorganism it hits, leaving it unable to reproduce. The microbe is still in the glass you drink; it simply cannot make you ill. Nothing dissolved is affected, and nothing suspended is removed.

Important

UV only works on water it can shine through. If your supply runs cloudy after rain, or carries visible sediment, particles shadow the microbes and the lamp's kill rate drops sharply. That is why a UV purifier without a sediment pre-filter in front of it is a poor design, not a bargain.

The decision rule, in the order you should apply it

Step 1 — Buy a digital TDS meter for about ₹300 and measure your supply. Do it twice: once in summer, once in monsoon. If the two readings differ by more than 150 ppm, design for the higher one.
Step 2 — Check whether your district has a documented arsenic, fluoride or nitrate problem. If it does, buy RO and stop reading. These contaminants are invisible and tasteless, and can be present at a perfectly ordinary TDS reading.
Step 3 — Under 200 ppm and no contaminant concern → UV+UF. You will spend less up front, less each year, and waste no water.
Step 4 — 200-300 ppm → either technology is defensible. UV+UF is the cheaper and more environmentally sensible call.
Step 5 — Over 300 ppm → RO, with UV behind it, and insist on a working TDS controller so the output does not land under 40 ppm.
Step 6 — Borewell, tanker or unknown → RO+UV, sized to the worst reading you have personally measured.

Running cost over five years

This is where the comparison stops being theoretical. The figures below assume a typical four-person household in an Indian metro, filters changed on schedule rather than when the taste goes off.

	RO + UV	UV + UF
Purchase	₹14,000	₹8,500
Filter sets (5 yrs)	₹12,000	₹6,000
RO membrane (2 changes)	₹3,600	—
UV lamp (5 changes)	₹4,000	₹4,000
Service visits	₹5,000	₹3,500
Electricity	₹1,300	₹900
Five-year total	₹39,900	₹22,900

Tip

The ₹17,000 gap is real money, and on low-TDS municipal supply it buys you nothing. That is the single most common overspend in this category in India.

Why 'RO+UV' is usually the answer anyway — and when it is not

Most households above 300 ppm should end up with both, and that is what the market sells. RO handles the dissolved load; UV covers the case where the membrane develops a pinhole or the storage tank picks up contamination between services. Belt and braces, and the incremental cost of the UV stage on an RO unit is small.

The case where the honest answer is UV alone is narrower than the industry admits but far from rare: piped, treated, chlorinated supply in cities like Mumbai, Kolkata, Shimla, Guwahati or much of Kerala, where TDS routinely sits between 60 and 180 ppm. Fitting RO there strips calcium and magnesium, flattens the taste, wastes water and adds a membrane replacement every two years to solve a problem the water treatment plant already solved.

Frequently asked questions

Is RO better than UV?

Not universally — they do different jobs. RO is better if your TDS is above 300 ppm, your source is groundwater, or there is any heavy-metal, arsenic or fluoride concern, because it is the only one of the two that removes dissolved contaminants. UV is better on treated municipal water under 200 ppm, because it kills microbes while keeping the minerals, wasting no water and costing roughly half as much to run.

Can I use only a UV purifier at home?

Yes, if your water is clear, treated municipal supply measuring under about 200 ppm TDS, with no known chemical contamination. Pair it with a UF or sediment stage so the lamp is working on clear water. If your supply is borewell, tanker-fed or seasonally turbid, UV alone is not adequate.

Does UV reduce TDS?

No. A UV lamp inactivates microorganisms and has no effect whatsoever on dissolved solids. If a salesperson tells you a UV purifier will bring your TDS down, they are either mistaken or selling you something else under a UV label.

Which is cheaper to run, RO or UV?

UV, by a wide margin. A UV+UF purifier costs roughly ₹1,200-2,000 a year in consumables; an RO+UV unit costs roughly ₹3,000-5,000 once you include the membrane, and additionally wastes 1-3 litres of water for every litre it purifies.

Do I need RO if my water TDS is 250?

At 250 ppm you are inside the BIS acceptable limit of 500 ppm and either technology is defensible. If the water tastes fine and there is no contamination concern in your area, UV+UF is the better-value choice. Buy RO at 250 ppm only if the reading climbs in summer, or if you have a specific chemical concern.