Updated October 2026.
Every year, a few days after the first heavy rain, somebody walks up to our counter holding a steel glass or a plastic bottle of their tap water. It's cloudy, or it smells a bit off, or a child at home has had a bad stomach, and they want the strongest purifier we've got. More often than not the first words are "give me a good RO".
Sometimes that's exactly right. Often it isn't. So here's the conversation we have across the counter every rainy season, written down. Why water gets riskier when the rains come, what RO, UV and UF each do, the one number that decides whether you need RO at all, what we'd correct from the old version of this page, and the purifiers we'd put in your kitchen.
Do you need an RO water purifier for the rainy season?
You need protection against germs in the rainy season, and you need RO only if the water reaching your home is also high in dissolved salts. Those are two separate problems, and the monsoon makes only the first one worse.
People ask us for an RO when what they mean is "make this water safe". RO is one way to do that, but it's the heavy tool. It forces water through a membrane fine enough to hold back dissolved salts as well as germs, which is brilliant for salty borewell water and wasteful for water that was never salty to begin with. UV and UF purifiers deal with the germs that the rains bring and leave the salts alone.
So the honest first question isn't which brand. It's what's in your water. We'll show you how to find out in two minutes further down, and once you know, the choice of RO water purifier, or no RO at all, mostly makes itself.
Why does drinking water get riskier in the monsoon?
Because heavy rain washes sewage and soil into pipes, tanks and groundwater, and germs travel with it. Leaky joints in old supply lines pull in dirty water when pressure drops, overhead tanks collect runoff, and borewells near drains pick up whatever seeps down.
The World Health Organization lists the diseases that contaminated drinking water carries: diarrhoea, cholera, dysentery, hepatitis A, typhoid and polio. It estimates that microbiologically contaminated drinking water causes about 505,000 diarrhoeal deaths a year worldwide (WHO drinking-water fact sheet).
Closer to home, a study in Clinical Infectious Diseases that drew on a civil hospital in Chandigarh noted a seasonal peak of typhoid fever there during the monsoon months, May to September (Clinical Infectious Diseases, 2021). That's one hospital, not all of North India, but it matches the pattern every family doctor in Delhi will describe to you.
What we see in the shop follows the same calendar. The calls about yellow or muddy water from the tap, the purifier that suddenly needs its filter changed after only a few months, the family who never thought about water until somebody fell ill. They bunch up in the weeks after the rains arrive, every single year.
RO, UV or UF: what's the difference?
RO removes dissolved salts and germs, UV kills germs without removing anything, and UF strains out germs and fine dirt but lets salts through. Most purifiers combine two or three of these, and the combination is what you're really choosing.
| RO (reverse osmosis) | UV (ultraviolet) | UF (ultrafiltration) | |
|---|---|---|---|
| How it works | Pushes water through a very fine membrane under pressure | Shines UV light on the water to stop germs multiplying | Strains water through a hollow fibre membrane |
| Bacteria and viruses | Held back by the membrane | Deactivated, though they stay in the water | Bacteria and cysts strained out |
| Dissolved salts (TDS) | Removed | Not touched | Not touched |
| Mud and cloudiness | Removed, but clogs the filters faster | Not removed, and murky water weakens UV | Removed |
| Sends water to the drain | Yes | No | No |
| Needs electricity | Yes | Yes | No, on its own |
| Best for | Borewell, tanker or salty supply | Low TDS piped supply, paired with UF | Low TDS piped supply, paired with UV |
| Typical price band | Under Rs 10,000 to Rs 20,000 and up | Under Rs 10,000 as UV plus UF | Under Rs 10,000 as UV plus UF |
That row about mud matters more than it looks in the rainy season. UV needs clear water to work, because the light has to reach every germ. Good UV purifiers put a sediment and carbon stage in front for exactly that reason. If your monsoon tap water is visibly muddy, the pre-filters are doing hard labour, and they'll need changing sooner than the box says.
What TDS level needs an RO water purifier?
Water above 500 mg per litre of TDS is where RO earns its place, and below that a UV plus UF purifier usually does the job. TDS means total dissolved solids, the salts and minerals dissolved in the water, and it's measured in mg per litre, which is the same number as ppm.
The 500 figure isn't ours. India's drinking water standard, IS 10500, sets 500 mg per litre as the acceptable limit for TDS and allows up to 2,000 only when there's no other source available (IS 10500:2012 limits, as published by IIT Kanpur). The National Green Tribunal used the same line in 2019, when it told the environment ministry to stop RO use where TDS is under 500 and to make manufacturers recover at least 60% of the water they treat (Down To Earth). The Supreme Court stayed a later version of that ban direction in 2022 (Verdictum). However the courts finally settle it, the logic behind it is the advice we give anyway.
Finding your number is easy. A pocket TDS meter costs very little, and plenty of purifier installers carry one. Fill a clean glass from the tap you drink from, dip the meter in, and read it. Do it once in the dry months and once after the rains if you can, because a supply that mixes sources can shift.
Where your water comes from tells you a lot before you even test it. Piped supply that's been treated at a plant usually reads low. Borewell water is a different story, at least in our part of town. The Central Ground Water Board's brochure for West Delhi, where our showrooms are, describes the district's groundwater as medium to highly saline, says the deeper water is saline, and flags higher fluoride and iron at Nangloi (CGWB West District brochure). Tanker water changes from one delivery to the next. If you're on a borewell or a tanker, plan on RO. If you're on piped supply that tests low, you probably don't need it.
Does RO water lose its minerals, and does that matter?
Yes. An RO membrane takes out most of the calcium and magnesium along with the salts, which is why good RO purifiers add some back. A review in Cureus put RO's removal at around 97% of calcium and 96% of magnesium (Cureus, 2023).
We have to correct the old version of this page here. It said that drinking purified water "offers calcium and magnesium", in a post recommending RO. For RO water that's the wrong way round, and we'd rather fix it out loud than leave it standing. The old list also put two water ionizers at the top of a list of RO purifiers, and ionizers aren't RO machines at all. One more pick on it was a UV and UF purifier, not an RO. We've rebuilt the whole thing from the specification sheets up.
How much the lost minerals matter is a fair argument, and most of what your body needs comes from food rather than the glass. But flat-tasting RO water is a real complaint we hear, and it's easy to avoid. Look for one of two features on an RO purifier:
- A TDS controller. It sends a small share of the water through UF instead of RO and blends it back in, so some of the natural minerals stay.
- A mineral or copper stage. A cartridge after the membrane that adds minerals back to the purified water.
Either one does the job. Ask the installer to set a TDS controller sensibly rather than as high as it'll go, because blending too much defeats the point of buying RO.
How much water does an RO purifier waste?
Every RO purifier sends some water down the drain, and on older designs it used to be most of it. When the National Green Tribunal heard the case in 2019, the association of RO manufacturers admitted that recovery under the earlier norms wasn't more than 20%, which means four litres in every five went to waste (Down To Earth).
Newer machines do much better, and some brands now publish recovery figures on their spec sheets. It's worth asking for that number when you compare two RO water purifier models side by side, along with the maximum input TDS each one is rated for.
The practical aside nobody puts in a brochure: the reject water isn't dirty, it's just salty. Run the drain pipe into a bucket and it'll mop the floor, flush the toilet or wash the car perfectly well. We tell every RO buyer this, and the ones who do it say they stop feeling guilty about the drain almost at once. Don't use it on pot plants if your water's very salty, though, because the salts build up in the soil.
Is boiling water enough in the rainy season?
Boiling kills the germs, so for safety alone, yes, a rolling boil works. The WHO says that heating water to a rolling boil is enough to inactivate the bacteria, viruses and protozoa that cause disease (WHO boil water technical brief).
Where boiling falls short is everything else. It doesn't remove salts, so borewell water stays salty, and it doesn't clear mud. It costs gas every day, the water has to cool before anybody drinks it, and once it sits in an open jug it can pick up germs all over again. We've got nothing against boiling, and during a power cut it's the right thing to do. Most families we talk to are simply tired of doing it three times a day for half the year.
How often should you service a water purifier around the monsoon?
Follow the filter life on your purifier, and if a service is due anywhere near the rains, get it done just before they start rather than after. Cartridges are rated by litres or by months, whichever comes first, and muddy monsoon water uses up the sediment and carbon stages faster than clean water does.
The signs a purifier needs attention are easy to spot once you know them. The flow drops to a trickle, the taste changes, the tank takes much longer to fill, or a service light comes on and stays on. An RO membrane wears with use too, so don't stretch it past what the manufacturer recommends.
The most common failure we see isn't a faulty machine. It's a filter left in long after its life ran out, quietly doing less every month while the family assumes it's fine. If you can't remember when your purifier was last serviced, that's your answer.
Which water purifier do we suggest at the counter?
One of these five, and which one depends almost entirely on your TDS reading and where your water comes from. We've put them in the order we'd walk you along the shelf, from piped supply to the hardest borewell water.
Kent Maxx Plus B UV+UF Water Purifier
The one we suggest when the TDS meter reads low and somebody walks in asking for RO anyway. Just under Rs 10,000. It's UV plus UF with an activated carbon pre-filter, so it deals with the germs that the rains bring without stripping minerals or sending a drop to the drain. It holds 7 litres, purifies at up to 60 litres an hour, draws just 36 W, and has a UV fail alarm that tells you when the lamp's weakening. Kent adds an alkaline and copper stage too. We sell it for the purification, and for low TDS piped supply it's the right machine.
Aquaguard Sure Champ RO+UV 1X Water Purifier
The sensible first RO for a borewell or tanker home on a budget. Under Rs 10,000. RO plus UV, rated for input water up to 2,000 ppm TDS, with a cartridge life of up to 6,000 litres or one year and LED alerts for service and filter life. It mounts on the wall or sits on the counter. This is the one we point to when the meter reads in the high hundreds and the family wants RO without stretching the budget.
LG WW132NF RO Water Purifier
For the person who doesn't like the idea of drinking water sitting in plastic. In the mid Rs teens. LG lists an 8 litre stainless steel tank with a 10 year tank warranty, an outside sediment filter with an anti-scalant module, a sediment and carbon filter, the RO membrane and a post carbon filter, plus LG's Digital Sterilizing Care for the water path. Its spec sheet doesn't list a UV stage, so the steel tank is its answer to keeping stored water clean. It's wall mounted and made in India.
Kent Grand Plus RO+UV+UF Water Purifier
The one for a big family that worries about the drain. In the high Rs teens. RO, UV and UF with a TDS controller, a UV LED inside the 9 litre tank to keep stored water clean, and up to 20 litres an hour. Its Zero Water Wastage system sends the reject water back for household use instead of down the drain. If someone has read about RO wastage and nearly talked themselves out of buying one, this is usually where the conversation ends up.
AO Smith Z2 Pro Under Counter RO Water Purifier
For the hardest water and the tidiest kitchen. Just under Rs 20,000. AO Smith lists it as 100% RO with seven stages, a copper fortified mineralizer to put minerals back, and a side stream membrane rated for TDS up to 2,000 ppm. It stores 6 litres for a family of three to eight, sits under the counter with its own faucet, warns you before the filters need changing, and carries a one year comprehensive warranty that includes the membrane. It's the one we suggest for deep borewell water in the western colonies, and for anyone who doesn't want a box on the wall.
Where can I buy an RO water purifier online in Delhi NCR?
You can buy an RO water purifier, or a UV and UF one, online from us with delivery across Delhi NCR, or come into one of our showrooms and see them side by side. The full range sits in our water purifier collection, from UV and UF models to under counter RO.
Our advice before you spend anything, and it costs us nothing to give it. Know three things when you come in. Your TDS reading, where your water comes from, and how many people drink from the tap. With those we can tell you in two minutes whether you need an RO water purifier at all. We've been an appliance retailer in this city since 1981, and we talk people out of RO about as often as we talk them into it. Then, whichever machine you pick, put the service date in your phone and get it done before the rains, every year. A well kept UV purifier on the right water will serve you better than a neglected RO on any water.
More water and geyser guides
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