Are you worried about water quality this monsoon and thinking of switching to RO? Or already have one and wake up every morning to drink RO water, assuming it's the healthiest choice?

Well, whichever side you're on, pause. And understand that the widespread perception that RO purifiers are the only way to ensure safe drinking water is misleading.

According to a report by the National Institute of Hydrology (NIH), Roorkee, reverse osmosis (RO) purifiers are not the right choice for every household. The institute says consumers should choose a water purification system based on the quality of their water, not marketing claims.

So, when do you actually need an RO purifier?

WHEN DO YOU NEED AN RO PURIFIER?

Experts and government reports point to just two situations where an RO purifier is necessary.

The first is when your source water has Total Dissolved Solids (TDS) above 500 mg/L. TDS measures the amount of dissolved minerals, salts and metals in water, expressed in parts per million (ppm) or mg/L.

The ideal TDS range for drinking water is 150-250 ppm. Water with TDS above 500 ppm generally requires treatment. The second is when laboratory testing confirms contamination from fluoride, arsenic, iron, heavy metals or pesticide residues.

Delhi-based science communicator and surgical gastroenterology specialist Dr Anshuman Kaushal said that outside these two situations, an RO purifier is unnecessary.

WHY RO ISN'T ALWAYS THE BEST CHOICE

If your water doesn't have high TDS or confirmed chemical contamination, an RO purifier may do more harm than good, both for your health and the environment.

It strips away essential minerals. RO technology removes not only harmful contaminants but also beneficial minerals such as calcium and magnesium.

According to the NIH report, RO-treated water can reduce calcium levels below 20 mg/L and magnesium below 10 mg/L—both lower than the World Health Organization's recommended health-benefit minimums. This is significant because more than 70% of Indian adults are already calcium deficient, meaning RO could further reduce mineral intake.

Dr Anshuman Kaushal said “the WHO's 2005 Rolling Revision report on demineralised water warns that long-term consumption may be associated with cardiovascular disease, bone demineralisation and higher rates of hypertension.”

He added that while calcium and magnesium should primarily come from food, the concern is greater for people with poor diets who consume very low-mineral water over many years.

RO also alters the taste of water by significantly reducing its mineral content and TDS.

Wastes a huge amount of water

The environmental cost is equally concerning.

For every 1 litre of water entering a typical RO purifier, only about 250 ml becomes drinking water. The remaining 750 ml is discharged as reject water—meaning nearly 75% of the water is wasted.

Dr Kaushal pointed out that the National Green Tribunal (NGT), in a 2019 order, directed the Environment Ministry to ban RO systems where TDS is below 500 mg/L and to mandate at least 60% water recovery. The Bureau of Indian Standards (BIS) has also proposed efficiency standards, but these have not been strictly enforced.

"Responsibility should sit with manufacturers through mandatory labelling, regulators through enforceable recovery norms, and municipal bodies jointly—not separately," he said.

He added that rejected water can be reused for mopping, gardening and toilet flushing, but very few households actually do so.

SHOULD YOU SWITCH TO UV OR UF?

Not necessarily. The right purifier depends entirely on your water source. A UV purifier is suitable for households receiving municipal or piped water with low TDS (below 300 mg/L) but where there is still a risk of microbial contamination.

UV light destroys bacteria and viruses but does not remove dissolved salts or suspended particles.

A UF (Ultrafiltration) purifier works well when water has microbial contamination but low dissolved solids. It is also useful in areas with unreliable electricity because it operates without power.

UF uses a hollow membrane to remove bacteria, viruses and suspended particles, and is often paired with UV technology for better protection.

Also, there are multi-stage systems that combine RO, UV and UF. They are useful only where water is both high in TDS and microbiologically unsafe. For example, households using borewell water mixed with municipal supply, a situation common in some semi-urban areas.

For clean municipal water, experts say such multi-stage systems are often not required.

WHAT SHOULD YOU DO?

The answer isn't to automatically buy an RO purifier or avoid one altogether.

“In fact, it provides safe drinking water in areas where the water quality is poor” according to Dr. Reetesh Sharma, Chairman Nephrology \& Kidney Transplant, Yatharth Super Speciality Hospital Faridabad.

So always test your water first.

You can check TDS using an inexpensive meter or get your water tested at an independent laboratory. "A 300 TDS meter and a one-time 500 microbial lab test will tell you more than any brand advertisement," said Dr Kaushal.

Only after knowing your water quality should you decide which purifier to go for in case needed.

- Ends

Published By:

Nabeela Khan

Published On:

Jul 22, 2026 10:00 IST