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RO vs UV vs UF: which water purifier does your home actually need?

Diagram comparing reverse osmosis, ultraviolet and ultrafiltration purification stages

The one measurement that decides everything

Buy a TDS meter before you buy a purifier. It costs around ₹400, takes ten seconds, and tells you which of these three technologies you need. Skipping this step is how people end up with an RO unit on 150 TDS municipal water, wasting three litres for every litre they drink.

What each one actually does

Reverse osmosis (RO) pushes water through a membrane fine enough to block dissolved salts, heavy metals and hardness. It is the only one of the three that lowers TDS. It also rejects a large share of the water as brine, and needs electricity and reasonable input pressure.

Ultraviolet (UV) shines light through flowing water to kill bacteria and viruses. It changes nothing you can taste, removes nothing dissolved, and needs water that is already clear to work — UV cannot penetrate cloudy water properly.

Ultrafiltration (UF) is a physical filter with pores small enough to trap bacteria, cysts and sediment. It needs no electricity, wastes nothing, and like UV leaves dissolved salts entirely alone.

Reading your result

  • Under 200 TDS — UV or UF is enough. RO is money and water thrown away.
  • 200 to 500 TDS — UV+UF usually covers it, unless hardness is scaling your taps and kettle.
  • Above 500 TDS — you need RO. Nothing else lowers dissolved solids.
  • Above 2,000 TDS — check whether domestic RO is rated for your input at all. Many are not, and running them out of spec kills the membrane early.

What the sales visit will tell you

A brand demonstrator will show you an electrolysis trick where a probe turns your tap water brown and the purified sample stays clear. This demonstrates electrode corrosion, not water quality, and it works on perfectly safe water. Ignore it and read your meter.

Common questions

Do I need RO if my water is already clear?

Clarity tells you nothing about dissolved salts. Water at 900 TDS looks identical to water at 90 TDS. Test with a TDS meter before deciding — clear water can still be hard water.

Is RO water unhealthy because it removes minerals?

RO removes calcium and magnesium along with the salts you want gone. Most units add a mineral or taste-adjustment stage to compensate. The mineral contribution of drinking water is small compared with food, so this matters less than marketing suggests — but on soft water there is no reason to strip and re-add in the first place.

How much water does RO waste?

Typically 2 to 3 litres rejected per litre purified on domestic units. Some models let you route reject water to a storage bucket for mopping or flushing, which is worth setting up.

Can UV alone make borewell water safe?

No. UV kills bacteria and viruses but does nothing to dissolved salts, hardness or heavy metals. On borewell water above 500 TDS, UV alone leaves the actual problem untouched.

Ready to choose?

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