Test method
How we test water purifiers
The uses we score and the tests we run on every water purifier: output TDS from hard water, reject water, 20 L fill time, noise and hot water speed.
Every water purifier we review is installed in a real Indian kitchen or office pantry and run on the household’s own supply for four to ten weeks, on the unit we bought or borrowed. RO purifiers are tested on borewell or tanker water at about 450 and 900 ppm TDS and then on a salt-spiked 1,500 ppm sample, so the output readings mean the same thing for every model. We also measure what each RO purifier sends down the drain, because reject water is the cost most buyers never see on the box.
Hot water purifiers get the same TDS tests plus hot water tests: the first cup from cold, cups per hour, the real temperature at each setting, standby energy and the child lock. Each test result in a review links back to the matching test on this page.
What we score
- Borewell and tanker water
- How far it brings down TDS from 450 to 1,500 ppm hard water, and whether that stays inside the brand's rated input limit.
- Low-TDS municipal water
- Whether a municipal supply below about 300 to 500 ppm needs RO at all, or whether a UV or UF purifier that wastes no water is enough.
- Large-family drinking volume
- How quickly it fills a 20 L can or a run of bottles, judged from fill time, tank size and the brand's stated purification rate.
- Chai, tea and formula
- For hot water purifiers: how fast the first hot cup arrives, how many hot cups it gives in an hour and how well each temperature setting matches its label.
The tests
-
Output TDS from 450 ppm input
We feed the purifier water at about 450 ppm TDS, the low end of a typical Indian borewell or tanker supply, and read the purified output with a handheld TDS meter after the tank has refilled.
-
Output TDS from 900 ppm input
We feed the purifier hard borewell water at about 900 ppm TDS and read the purified output with a handheld TDS meter after the tank has refilled. This is the reading we compare first across RO purifiers.
-
Output TDS from 1,500 ppm input
We raise the input to about 1,500 ppm by adding a salt solution, to mimic a tanker or summer borewell spike, and read the purified output with a handheld TDS meter.
-
Reject water at 450 ppm input
For RO purifiers, we collect the drain water in a graduated jug while the purifier makes purified water from 450 ppm input, and report litres of reject for every litre purified.
-
Reject water at 900 ppm input
The same reject measurement as at 450 ppm, repeated with 900 ppm input. Reject water rises as input TDS rises, so this shows the real waste on hard borewell supply.
-
Time to fill a 20 L can
Starting from a full storage tank, we draw water into a 20 L can and time how long it takes to fill. The tank gives the first few litres; the rest comes at the membrane's pace.
-
Pump noise at 1 m
We record the sound level at 1 m from the unit while the pump runs to refill the tank after a heavy draw.
-
Power while the pump runs
We plug the purifier into a plug-in power meter and read the wall power while the pump runs, which tells you what size of inverter will carry it through a power cut.
-
First hot cup from cold
For hot water purifiers, we start from a cold unit and time how long it takes to dispense a 150 ml cup at the hottest common setting, 80 °C where the purifier has one.
-
Hot cups in an hour
For hot water purifiers, we draw 150 ml cups at the hot setting and count how many we get in an hour before the output falls below 75 °C.
-
Temperature at the tap
For hot water purifiers, we check each hot and warm setting with a thermometer at the nozzle and report the range we read against the temperature the brand lists.
-
Standby energy
For hot water purifiers, we log energy use on a plug-in meter over seven days of normal household use and report the daily average spent keeping the unit ready.
-
Child lock on the hot tap
For hot water purifiers, we check whether a child lock is fitted and whether it stops hot water when the panel is pressed once by accident, including a reach at child height.