# RO vs UV vs UF water purifier: which one do you need?

> RO, UV and UF purifiers solve different problems. Pick by your water's TDS and source: RO for hard borewell water, UV or UF for soft municipal supply.

URL: https://best.bloomsynth.com/water-purifiers/ro-vs-uv-vs-uf/
Published: 2026-11-15
Publisher: Best in Budget (https://best.bloomsynth.com)

## Quick answer

Choose by your water, not by the number of stages on the box. If the TDS is above about 500 mg/L, as with most borewell and tanker water, you need RO. If it is below that, as with most municipal supply, a UV purifier with a sediment and carbon filter is enough and wastes no water. UF suits the same low-TDS water where power cuts are common, because it works without electricity.

Every purifier box lists RO, UV, UF and a few more letters, as if more were always better. They are three different tools. Which one you need depends on what is in your water.

## What each technology does

| | RO | UV | UF |
|---|---|---|---|
| Removes dissolved salts (TDS), hardness | Yes | No | No |
| Removes heavy metals such as arsenic, lead, fluoride | Yes | No | No |
| Deals with bacteria | Yes | Yes | Yes |
| Deals with viruses | Yes | Yes | Not reliably |
| Needs electricity | Yes | Yes | No |
| Wastes water | Yes | No | No |

**RO (reverse osmosis)** pushes water through a membrane with pores so fine that dissolved salts and metals cannot pass. It is the only one of the three that lowers TDS. The price is water: a typical home RO sends two litres or more down the drain for each litre it purifies, and it needs power and good inlet pressure.

**UV (ultraviolet)** shines a UV lamp on the water as it flows past. The light inactivates bacteria and viruses so they cannot multiply. It removes nothing: salts, chemicals and mud pass straight through, which is why UV purifiers always have a sediment filter and a carbon filter in front of the lamp.

**UF (ultrafiltration)** is a membrane with larger pores than RO. It blocks bacteria, cysts and fine particles but lets dissolved salts through. It works on gravity or tap pressure alone, with no electricity.

## Start with your water's TDS

TDS, total dissolved solids, is the amount of salts and minerals dissolved in the water, measured in mg/L (the same as ppm). A pocket TDS meter costs little and gives a reading in seconds; many purifier technicians carry one too.

- **Below about 200 mg/L:** soft water, usually a river-fed municipal supply. Use UV, or UF if power is unreliable. RO would strip out minerals you want and waste water for no benefit.
- **200 to 500 mg/L:** still within the acceptable limit of the Indian standard. UV with good pre-filters is enough for treated municipal water. Consider RO only if the water tastes salty or your source is mixed.
- **Above 500 mg/L:** borewell, tanker or mixed supply in most cities. You need RO. Pick one with a TDS controller or mineraliser so the output does not taste flat.

If your home gets municipal water on some days and tanker or borewell water on others, choose for the worst water you get: an RO+UV purifier with a TDS controller.

## What about "RO+UV+UF" models?

In a combined purifier the RO membrane does the heavy work, the UV lamp is a second safeguard against germs, and the UF membrane often treats the portion of water that bypasses RO to keep some minerals. The combination makes sense for high-TDS water. For low-TDS water it is the wrong purifier with extra parts to service.

## Running costs to check before buying

- **Filters and membrane:** sediment and carbon filters are changed about once a year, and an RO membrane every two to three years, sooner with very hard water. Ask what the yearly service costs before you choose a model.
- **Water wastage:** if you buy RO, collect the reject water in a bucket for mopping or flushing.
- **Storage tank:** a tank of 6 to 8 litres suits most families of four. With UV, do not leave water sitting in the tank for days.

More guides on choosing a purifier are in the [water purifiers](/water-purifiers/) section, and [how we choose products](/about/) explains where our information comes from.

## Frequently asked questions

### What TDS level needs an RO purifier?

The Indian standard for drinking water (IS 10500) sets 500 mg/L as the acceptable limit for total dissolved solids. Above that, RO is the only home technology that brings it down. Below it, RO is not needed for TDS.

### Does a UV purifier reduce TDS?

No. UV light inactivates bacteria and viruses but leaves everything dissolved in the water exactly as it was. The TDS reading is the same before and after a UV purifier.

### Is RO water bad because it removes minerals?

RO removes most dissolved minerals along with the harmful salts, which makes very low TDS water taste flat. Many RO purifiers add a TDS controller or a mineral cartridge to bring the taste back. If your water is already below 500 mg/L, you avoid the question by not using RO.

### Can I use a UF purifier for borewell water?

Only if the borewell water has low TDS and no chemical contamination, which is uncommon. UF removes germs and particles but not dissolved salts, hardness, fluoride or arsenic.