Do you actually need reverse osmosis?
Reverse osmosis is sold as the top of the range, as though more filtration were always better. It is not a ladder. RO does one specific job superbly and charges you for it whether or not you need it done — and a two-minute test tells you which case you are in.
What reverse osmosis actually removes
Osmosis is water moving across a semi-permeable membrane towards the saltier side. Reverse osmosis is what happens when you apply enough pressure to push it the other way: water molecules through, dissolved ions left behind. The separation is at the scale of a fraction of a nanometre, far below anything a conventional filter does, and it is the reason RO is the only stage in a domestic machine that reduces a TDS reading.
What that buys you is specific and genuinely valuable where it applies: dissolved salts, calcium and magnesium hardness, nitrates, fluoride, arsenic and most heavy metals. A domestic membrane in good condition typically rejects the large majority of dissolved solids — high enough that a 900 mg/L feed comes out as something in the low tens. Nothing else in the box does that. Carbon adsorbs; UV sterilises; ultrafiltration screens. None of the three removes a dissolved salt.
Note what the figure shows about the membrane's position: it sits behind the pre-filters for a reason. Chlorine attacks a thin-film composite membrane, and sediment blinds it. The carbon and sediment stages ahead of it are not there for your taste buds; they are there to keep the expensive part alive. That is also why skipping a pre-filter change to save money is a false economy — it is the membrane that pays.
When you genuinely need it
RO earns its keep when the problem is dissolved. In practice that means one of these:
- A TDS reading meaningfully above the BIS acceptable limit of 500 mg/L, or above the 1,000 mg/L limit in the Chinese GB 5749 standard. Large parts of northern and western India sit well above both on groundwater.
- Borewell or other untreated groundwater, where nitrates from agriculture, geological fluoride or arsenic are possible and none of them can be tasted, smelled or seen.
- Brackish or coastal supply, where sodium chloride makes the water taste salty and no amount of carbon will touch it.
- Water hard enough to scale a kettle in weeks, if you want that hardness out of your drinking water rather than just softened for washing.
- A known local contamination problem confirmed by a lab test — heavy metals in particular.
This is exactly the reading the water finder is looking for. Answer that your supply is borewell, or that your kettle scales fast, and it treats RO as effectively mandatory: a non-RO machine is pushed so far down the ranking that it will not be recommended to you at all. That is deliberate. Suggesting a gravity filter to someone on 1,200 mg/L groundwater would be a bad recommendation dressed up as a cheap one.
When you probably do not
The common case against RO is a low-TDS municipal supply where the complaint is taste or peace of mind. If your meter reads 100 to 250 mg/L and the water smells faintly of chlorine, you do not have a dissolved-solids problem. You have a chlorine problem, and activated carbon solves it for a few hundred rupees or a hundred yuan a year.
| What you notice | What it usually is | What handles it |
|---|---|---|
| Swimming-pool smell | Chlorine residual | Activated carbon |
| White scale in the kettle | Calcium and magnesium hardness | RO (or a softener for washing) |
| Salty or bitter taste | High dissolved salts | RO — nothing else |
| Worry about bugs, taste is fine | Microbial risk | UV, ultrafiltration, or boiling |
Two of those rows are worth expanding. A UV lamp inactivates bacteria, viruses and protozoa by damaging their DNA, which is effective and cheap to run — but it needs the water to be clear enough for the light to reach through, it removes nothing, and it leaves no residual protection downstream of the lamp. Ultrafiltration uses a hollow-fibre membrane with pores in the region of 0.01 to 0.1 µm, which physically retains bacteria, cysts and most viruses while passing every dissolved salt straight through. Both are real answers to microbial risk. Neither is an answer to TDS.
The reverse also holds, and it is the part people forget: an RO membrane is not a licence to stop worrying about microbiology. Membranes can develop pinhole defects, and the tank or tubing downstream of one can harbour growth. That is precisely why four of the six Indian machines in this catalogue are sold as RO+UV combinations rather than RO alone — the lamp guards the storage tank that the power cuts make necessary.
Why this catalogue is almost entirely RO
Being plain about it: of the 13 water purifiers on this site, 12 are reverse osmosis and one is a non-electric gravity filter. There is no UV-only machine here and no UF-only machine here, so this page cannot and does not offer you a product comparison between the three technologies. It explains them because the explanation is what tells you whether the RO you are being sold is the right answer.
The reason the list looks like that is the two supplies it serves. Across much of India the domestic water question is groundwater with high TDS and hardness, and that is a membrane problem by definition — 12 of the 13 machines here are rated for high-TDS feed, and the single one that is not is the gravity filter. In China the municipal supply is treated and pressurised, but under-sink RO became the default domestic appliance regardless, and the market now offers essentially nothing else at this price point.
If your reading comes back low and you are on treated municipal water, the honest conclusion may be that the cheapest row here — the ₹2,449 gravity filter, with no electricity, no plumbing and an 18-litre reservoir — does what you actually need. It is slow, at 3 L/h, and it does nothing about dissolved solids. On soft municipal supply, neither of those is a problem.
What unnecessary RO costs you
Three costs, in rough order of how much they annoy people.
Reject water
A membrane separates; the concentrated side has to go somewhere, and it goes down the drain. Older domestic RO commonly discarded two or three litres for every litre produced. Modern low-waste designs push that ratio much closer to parity, and 7 of the 13 machines here carry the low-waste or non-electric flag. If you live somewhere water is metered, rationed or tankered in, this is not a footnote. Low-waste machines for borewell water is the shortlist for people who need the membrane but not the waste.
Minerals you paid to remove
A membrane cannot tell a useful mineral from a harmful one; both are ions. RO water is therefore very low in calcium and magnesium, and it tastes flat as a result — flat enough that manufacturers add a stage to put some back. Six of the 13 machines here have a mineraliser, four Indian and two Chinese. Adding minerals back at the last stage after spending money to take them out is a slightly absurd sequence, and it is the honest signal that a membrane is over-treating water that did not need it. The taste side of this is covered in understanding TDS and hard water .
Upkeep and complexity
An RO machine has more cartridges, a pump, and a membrane that is the most expensive consumable in the box. This catalogue scores upkeep from 1 to 3, and the gravity filter sits at the cheapest level along with four RO machines — while the two most feature-rich units sit at the top of the scale. Every additional stage is another thing to buy on a schedule. Water purifier running costs puts numbers on it.
Deciding, in four steps
Take a TDS reading of your own tap
A handheld meter is the cheapest instrument in this category. Read the cold tap after it has run for thirty seconds, and read it again on a different day — supplies vary, particularly where a building tank is involved.
Test hardness separately
A strip tells you calcium and magnesium specifically. High TDS with low hardness is a salt problem; high hardness is a scale problem. They call for the same machine but for different reasons, and only one of them shows up in your kettle.
Ask what your supply is, not just what it reads
Municipal, borewell, or a building tank. Untreated groundwater justifies a membrane even at a moderate TDS reading, because the contaminants that matter most in groundwater are the ones a meter cannot see.
Then choose — and size the reject ratio to your situation
If RO is the answer, the remaining question is which one: tank or tankless, mineraliser or not, low-waste or not. How to choose a water purifier works through the rest of the decision, and the finder and the prepared shortlists do it for you.
Questions readers ask
- Is RO water unhealthy because it has no minerals?
- Drinking water is a minor source of dietary calcium and magnesium compared with food, so for most people on a normal diet this is a taste question rather than a nutrition one. It is a real taste question though, which is why 6 of the 13 machines here add a mineraliser stage.
- My municipal water tests at 150 mg/L. Do I need RO?
- Probably not for dissolved solids — that is comfortably inside the BIS acceptable limit of 500 mg/L. If the complaint is chlorine taste, carbon handles it; if it is microbial risk, UV or ultrafiltration handles it. A membrane would be solving a problem your reading says you do not have.
- How much water does an RO purifier waste?
- Older domestic machines commonly sent two to three litres to drain for every litre produced. Low-waste designs bring that much closer to one to one, and 7 of the 13 machines in this catalogue are flagged as low-waste or non-electric.
- Does RO remove bacteria and viruses?
- A membrane in good condition rejects them by size, but membranes can develop defects and anything downstream — tubing, a storage tank — can harbour growth. That is why four of the six Indian machines here pair RO with a UV lamp rather than relying on the membrane alone.
- Can I just use a UV or UF purifier instead?
- For microbial risk on low-TDS treated water, yes, and they are cheaper to run. But this catalogue has no UV-only or UF-only machine to sell you — it is 12 RO units and one gravity filter, because both markets it serves are dominated by supplies where a membrane is the usual answer.