RO vs UV vs UF: What Each Removes (Comparison Table)

RO, UV and UF are sold as if they were three grades of the same thing — good, better, best. They are not. They are three different tools that remove three different classes of problem from water, and the most expensive one is frequently the wrong one for your tap. Buying RO for clean municipal water is like buying a truck to carry a lunchbox.

This guide puts all three technologies in one honest chart, then explains what each one actually does inside the machine — so the next time a salesperson says "sir, RO is best", you can ask the only question that matters: best against what, exactly?

How to read this

Most homes confuse "safe" with "low TDS". Bacterial safety is independent of dissolved-salt count. UV makes water bacteriologically safe; RO additionally lowers TDS. UF is mechanical-only — no power, no salt removal.

So the chart above is really answering two separate questions. Question one: does your water carry dissolved salts and heavy metals (a TDS problem)? Only RO fixes that. Question two: does your water carry bacteria and viruses (a biological problem)? UV and UF fix that, and RO's membrane happens to block them too. Your water report tells you which questions apply to your tap.

What RO actually does

Reverse osmosis pushes water under pump pressure through a membrane with pores so fine that dissolved salt ions largely cannot pass. That is why it is the only technology of the three that lowers TDS — removing 90–98% of dissolved solids including heavy metals like lead and arsenic. It is also why it needs electricity, and why it rejects roughly 3 litres for every litre purified: the concentrated salts must be flushed away.

The cost of that power is over-purification. RO strips calcium and magnesium along with the sodium and nitrates, which is why pure RO water tastes flat and why a mineraliser or TDS adjuster stage matters in the 200–500 ppm band.

What UV actually does

A UV chamber is a light treatment, not a filter. Water flows past an ultraviolet lamp whose radiation destroys the DNA of bacteria, viruses and cysts, leaving them unable to reproduce — effectively dead. Nothing is physically removed: the water that enters is the water that leaves, minerals, TDS and all.

That makes UV ideal for low-TDS water with biological risk — the classic municipal-supply scenario where the source is treated but the building's storage tanks are not trustworthy. Its weaknesses are equally clear: it cannot fix taste, salts, or hardness, it needs electricity, and its lamp loses intensity with age and must be replaced roughly annually even though it still glows.

What UF actually does

Ultrafiltration is a fine mechanical sieve — hollow-fibre membranes with pores around 0.01 micron that physically trap bacteria, cysts and larger particles. Because it works on water pressure alone, gravity-fed UF purifiers run without electricity, which makes UF the only option of the three that keeps working through a power cut.

Its pore size is its limit. Viruses are smaller than most UF pores, so viral protection is only partial, and dissolved salts pass through untouched. UF shines as a polishing stage in combination units and as a standalone in low-TDS, low-risk supplies where its near-zero running cost — no lamp, no pump, minimal parts — is unbeatable.

The decision in four lines

• TDS below 200 ppm, trustworthy source and tanks: UF alone is adequate and nearly free to run
• TDS below 200 ppm, biological risk (old buildings, shared tanks): UV+UF — safety without stripping minerals
• TDS 200–500 ppm: RO with a TDS adjuster or mineraliser, so salts drop but taste survives
• TDS above 500 ppm, or any borewell/tanker dependence: full RO+UV+UF — nothing less removes what is dissolved in that water

Most common stack today

RO + UV + UF + post-carbon mineraliser is the default for 70%+ of urban Indian homes because feed water quality varies even within a building. The mineraliser re-adds calcium and magnesium that pure RO removes.

The layered stack also covers each technology's blind spot: RO handles the dissolved load, UV sterilises anything that slips past, UF physically removes the debris and dead organisms UV leaves behind, and carbon fixes taste. That redundancy is why combination units dominate — not because every home needs every stage every day, but because supply in most Indian cities cannot be trusted to stay in one category year-round.

Running costs over five years

Purchase price is the smaller half of the story. At typical metro market rates, a UF unit costs ₹400–1,000 a year to maintain, UV ₹800–1,800 (mostly the annual lamp), and RO ₹1,500–3,500 (sediment and carbon changes yearly, membrane every two to three years). Over five years, an RO unit's service bill often equals its purchase price; a UF unit's rarely crosses a quarter of it.

Add water cost to the maths: at a 3:1 reject ratio, an RO family consuming 12 litres a day sends over 13,000 litres a year down the drain unless the reject is reused. None of this argues against RO where TDS demands it — it argues against buying RO where it does not.

From the field

The most common mismatch seen across two decades of service work is RO installed on 100–150 ppm municipal water. The family paid more upfront, pays more every year, waters the drain daily — and the children slowly stop drinking plain water because it tastes like nothing. Meanwhile the borewell home next door runs a bare UV unit and wonders why the kettle scales up every month. Both bought on brand, not on water.

The single habit that prevents both mistakes costs ₹300: a pocket TDS meter used before purchase and monthly after. The chart in this guide plus one number from your own tap beats any showroom pitch. When the number and the technology match, service visits become routine maintenance instead of crisis calls.

When to call a professional

Reading your TDS, tasting for change, and checking flow are all yours. But choosing between these technologies for a borderline supply, diagnosing why output TDS is creeping up, or converting a unit (adding a UV stage, fitting a TDS adjuster) needs someone who opens these machines daily — a wrong conversion wastes more than it saves.

If your readings do not match what your technology should deliver, book a background-verified technician through a platform with fixed transparent prices, genuine parts and a 30-day service warranty. A proper visit starts with input and output TDS readings in front of you — insist on both, and the right recommendation usually writes itself.