How to choose a water purifier: test first, then buy

A water purifier is not a general-purpose safety device. Each stage inside it removes one narrow class of thing and is blind to the rest. Sediment filters catch grit. Activated carbon adsorbs chlorine, chloramine and many organic compounds that carry taste and smell. Ultraviolet lamps inactivate bacteria, viruses and protozoa but remove nothing at all. A reverse-osmosis membrane is the only part of a domestic machine that takes out dissolved solids — salts, hardness minerals, nitrates, heavy metals. Buy the wrong combination and you have paid for a stage that does nothing about your actual problem, and skipped the one that would have.

So the first purchase is not a purifier. It is a reading. A handheld TDS meter is the cheapest instrument in this whole category and takes about ten seconds to use; a hardness test strip costs less again. Between them they tell you whether your problem is dissolved solids, or taste and chlorine, or microbial risk, and those three point at different machines. Understanding TDS and hard water covers how to take the reading and, just as importantly, what it cannot tell you.

Add one piece of local knowledge the meter cannot supply: where the water comes from before it reaches you. Municipal supply is treated and usually carries a chlorine residual, which is why it often smells faintly of a swimming pool and why the residual is doing useful work right up to your tap. Borewell and other groundwater is untreated, and whatever the aquifer holds comes with it. A building tank sits in between: treated water that has then been stored, sometimes for days, in a container nobody has opened in a year.

Once you have a number, the technology follows almost mechanically. Dissolved solids need a membrane. Taste, chlorine and odour need carbon. Microbial risk needs UV or ultrafiltration, or a boil. Turbidity needs sediment filtration ahead of everything else, or the stages behind it clog early.

The important consequence is that RO is the only one of the four that changes a TDS reading. If your water tests at 900 mg/L, no amount of carbon or UV will move that figure by a meaningful amount. If it tests at 120 mg/L and simply tastes of chlorine, a membrane is solving a problem you do not have — and charging you for it every month. That argument is long enough to need its own page: do you need reverse osmosis works through when the answer is genuinely yes and when it is not.

One thing to be straight about: this catalogue holds 13 water purifiers, and 12 of them are RO. The thirteenth is a non-electric gravity filter. There are no UV-only or UF-only machines here to choose between, because both markets this site serves are dominated by supplies where a membrane earns its place — high-TDS groundwater across much of India, and a strong consumer preference for RO in China. Twelve of the 13 are rated to handle high-TDS water; the gravity unit is the one that is not.

Capacity is two numbers that people routinely confuse. Flow rate is how fast the machine makes purified water, in litres per hour. Storage is how much finished water it holds ready. Across the 13 machines here flow runs from 3 L/h to 160 L/h with a median of 20 L/h, and storage from 0 L to 18 L with a median of 4 L. Those two ranges are enormous, and which end you need depends far less on your household size than the marketing suggests.

Do the arithmetic. Drinking and cooking for four people is roughly 10 to 15 litres a day. A machine rated at 12 L/h covers that in about an hour of running. Flow rate almost never limits a household's daily drinking water. What it limits is how long you stand at the tap filling a pot — which is why the Chinese tankless machines chase big numbers and the Indian tank machines do not need to.

The Chinese ratings are quoted in gallons per day, which is where the 600G, 800G and 1000G badges come from. One US gallon is 3.785 litres, so a 1000G nameplate is 3,785 L per day, or about 158 L/h if it ran flat out for 24 hours. This catalogue lists that machine at 150 L/h, and every G-rated row here follows the same conservative arithmetic: the G number divided by about 6.7. Treat the badge as a laboratory figure taken at rated pressure and 25 °C. Cold feed water in January and an ageing membrane both pull real output below it.

This is the clearest structural difference in the catalogue, and it is not a matter of taste. It is a matter of what the electricity and the mains pressure do where you live.

All six Indian machines here carry a storage tank — 7, 7, 8, 9 and 10 litres for the five RO units, and 18 litres for the gravity filter. Power cuts are normal, and an RO membrane needs a pump to work. A tank means that when the power goes, you still have water. A 7-litre tank on a 12 L/h machine refills in about 35 minutes, so the tank is not a bottleneck in normal use; it is an insurance policy that happens to also smooth out the pauses.

Six of the seven Chinese machines hold nothing at all: 0 litres of storage, and flow rates from 90 to 160 L/h. Mains pressure is reliable, so they purify on demand, straight through, and the water you drink was made three seconds ago rather than sitting in a plastic tank since Tuesday. The seventh Chinese unit is the exception worth knowing about — a countertop dispenser with a 4-litre reservoir you fill by hand, which needs no plumbing at all and suits a rented flat.

The trade-offs are real on both sides. A tank is stored water, so it needs the tank kept clean and it takes cupboard space. A tankless unit is dependent on pressure and on power at the moment you want a drink, and the high-flow membranes that make it possible are physically larger. Storage tanks and flow rates goes through both in detail.

The purchase price is the smaller number. A domestic RO machine is a subscription: pre-filters typically want replacing every 6 to 12 months, the carbon stages on a similar cycle, and the membrane itself every 2 to 3 years — sooner on hard feed water, because the thing that scales your kettle also scales the membrane.

This catalogue rates upkeep on a simple 1-to-3 scale. Five of the 13 sit at the cheapest level, two at the most expensive, and the median is the middle. The two dearest to run are also two of the most capable — a hot-water RO in India and a 160 L/h flagship in China — which is the usual shape of this trade: the features that justify the price are the features that add cartridges.

Prices themselves differ by market and are not conversions of one another. The six Indian machines run ₹2,449 to ₹26,900 with a median of ₹15,999. The seven Chinese machines run ¥1,499 to ¥4,599 with a median of ¥2,099. Never read one as a translation of the other; they are different products for different supplies. The arithmetic of filters, membranes, electricity and reject water is in water purifier running costs .

If low upkeep is the thing you care about most, say so up front rather than discovering it a year in. There are prepared shortlists for exactly that: low running cost on municipal water and low running cost on borewell water under ₹15,000 .

1. 1

   Measure the space before you choose

   Under-sink units need the cabinet depth and a clear path for the cartridges to come out — you will be pulling them every 6 to 12 months, and a machine you cannot service is a machine that does not get serviced. Wall-mounted tank units need a stud or a masonry wall that will carry the unit plus 7 to 10 litres of water.

2. 2

   Check you have a feed, a drain and a socket

   Any RO machine needs three things: a cold feed it can tap, a drain for the reject line, and power. Missing any one of them changes the job from an hour to a plumbing call. The 4-litre countertop dispenser and the 18-litre gravity filter are the two rows here that need none of it.

3. 3

   Test your mains pressure if the unit is tankless

   Tankless RO relies on pressure to push water through the membrane. Chinese units assume a reliable municipal supply. If your pressure sags in the evening or you are on an upper floor of an older building, a booster pump or a tank model is the safer choice.

4. 4

   Find out who services it, locally, before you buy

   Consumables and callouts decide whether a purifier survives its third year. Ask what a membrane replacement costs and how long the part takes to arrive, in your city, not nationally. This is the single most common reason a good machine becomes a bad purchase.

5. 5

   Re-test after a month

   Take a TDS reading of the purified output once the machine has settled in and write it down with the date. That number is your baseline: when it starts climbing, the membrane is on its way out, and you will know months before the taste changes.

1. Test. TDS reading, hardness strip, and know whether your supply is municipal, borewell or a building tank.
2. Pick the technology the reading implies — not the one with the most letters on the box. See do you need reverse osmosis .
3. Size it. Daily litres for the household, then decide whether you need flow rate or storage. See storage tanks and flow rates .
4. Price the upkeep, not the box. See water purifier running costs .
5. Check it fits, that there is a drain and a socket, and that someone nearby services it.

And if you are here about the other machine in the house, the same logic — measure the problem, then buy for it — runs through how to choose an air purifier .