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The quick comparison
| RO | UV | UF | |
|---|---|---|---|
| What it does | Pushes water through a very fine membrane | Treats germs in the water with light | Holds back particles with a fine filter |
| Removes dissolved salts? | Most of them | No | No |
| Removes dirt? | Yes, along with its other filters | No | Yes, particles |
| Sends water down the drain? | Yes | No | Usually no |
| Needs power? | Yes | Yes | Some models do not |
| Usual starting point | High TDS, borewell | Low TDS municipal water | Low TDS, often paired with UV |
| Upkeep | Higher | Lamp to replace | Filter to replace |
Most purifiers on sale combine two or three of these. So the real question is whether your home needs the RO part. Your water answers that, not the number of stages printed on the box.
RO, UV and UF in plain words
RO means reverse osmosis. A pump pushes water through a very fine membrane. Clean water passes through, and the salts stay behind and go down the drain with some of the water. That is why RO is the one to look at when your water tastes salty or leaves heavy marks.
UV means ultraviolet. Water passes a lamp, and the light treats germs. Nothing is filtered out. Muddy water can block the light, so UV needs clean water going in. That is why it is often paired with a filter.
UF means ultrafiltration. It is a fine filter that holds back particles. It does not change the dissolved salts, so salty water stays salty.
TDS control appears on some RO units. It lets a small amount of water skip the RO stage to adjust TDS and taste. It depends on being set up for your water.
Start with TDS and your source
TDS means total dissolved solids. A pocket TDS meter is cheap and easy to use. Test on more than one day, because tanker and borewell water can change through the year.
The Indian drinking water standard, IS 10500, gives 500 mg/L as the acceptable TDS limit. It allows up to 2000 mg/L when there is no other source. A TDS number alone does not tell you if water is safe, so use the table below as a rough starting point, not as safety advice. A lab report on your own water overrides it.
| Your water | Start by looking at |
|---|---|
| Municipal, low TDS, tastes fine | UV and UF, no RO |
| Municipal, up to 500 mg/L, taste is a problem | RO with TDS control, or stay with UV and UF |
| Above 500 mg/L | RO |
| Borewell or tanker | Lab test first, then usually RO |
Wasted water
Only RO has this cost. It depends on the model and your TDS. An older, ordinary RO unit can reject two or more litres for each litre of drinking water.
Take an example family that uses 10 litres of drinking water a day, with a unit that rejects 2 litres for each litre it makes. That is 20 litres rejected daily, or 7,300 litres a year. Both figures are examples, so check the recovery figure on the listing you are looking at. You can collect the rejected water for mopping or flushing. It has more salts, so avoid using it on plants.
Running cost
Electricity is a small part of the bill. As an example, a 60 watt unit that runs 2 hours a day uses 3.6 units a month. At an example rate of ₹8 per unit, that is about ₹29. Your rate depends on your state and how much you use, so check your bill.
Filters and service cost more than power. Ask for the price of each part and how often it needs changing, including the RO membrane on an RO unit and the lamp on a UV unit.
Which should you choose?
Choose RO if your TDS is above 500 mg/L, your water tastes salty, or a lab test on your borewell or tanker water points to it. Accept that it needs a drain point and regular service.
Choose UV with UF if you are on municipal water with low TDS, the taste is fine, and you do not want to send water down the drain.
Choose RO with TDS control if your municipal water is under 500 mg/L but the taste bothers you, and you want a way to adjust it.
Wait and test if you do not know your source or your TDS. A meter costs far less than the wrong purifier.
Options to look at on Amazon
We have not tested these. Both include RO, so they suit the higher TDS and borewell rows above, not low TDS water. They are in no particular order, and the details come from the listing titles. Check the current price, warranty and reviews on Amazon.
| Product | Type |
|---|---|
| Aquaguard Delight Aquasaver | RO+UV+UF |
| KENT Supreme Plus | RO+UV+UF+TDS Control |
Before you buy
Check wall space, a nearby socket and a drain point. Ask who installs it, and confirm that an authorised service person covers your area. Then add the purchase price to a few years of filters and service, and compare that total, not only the price on the day.
The products in this comparison
Aquaguard Delight Aquasaver
KENT Supreme Plus
Read next
Common questions
Is RO always better than UV?
No. They do different jobs. RO removes most dissolved salts, and UV treats germs. If your TDS is low and your water tastes fine, RO may only add wasted water and service bills.
Do I need both UV and UF?
They are often sold together because they do different work. UF holds back particles and UV treats germs. Neither one removes dissolved salts.
Can I check my water with a TDS meter alone?
Only in part. A TDS meter shows the amount of dissolved solids. It does not show germs and it does not name the salts or metals present. That needs a lab test.