Is RO Water Really the Best Choice? What Science Says About Purifiers, TDS and Alternatives

Monsoon clouds are gathering and, like every year, the question pops up: should I switch to an RO purifier, or stick with what I have? Before you rush to the store, take a breath and remember that the idea ‘RO = pure water’ is a bit of a myth.

Recent findings from the National Institute of Hydrology (NIH) in Roorkee make it clear – you don’t need an RO system for every tap. The right purifier depends on the actual quality of your water, not on glossy ads promising miracles.

When does an RO unit become truly necessary? Experts point to just two scenarios. First, the water source has a Total Dissolved Solids (TDS) reading above 500 mg/L. TDS measures the total amount of salts, minerals and metals dissolved in water, expressed in parts per million (ppm). The sweet spot for drinking water sits between 150‑250 ppm; anything above 500 ppm usually needs treatment.

The second situation is when a laboratory test confirms the presence of specific contaminants such as fluoride, arsenic, iron, heavy metals or pesticide residues. Outside of these two cases, an RO system often does more harm than good.

Why RO isn’t always the best choice – it strips away minerals. The membrane doesn’t discriminate between harmful pollutants and beneficial calcium or magnesium. NIH data shows RO‑treated water can dip below 20 mg/L of calcium and 10 mg/L of magnesium – both lower than the World Health Organization’s suggested minimum for health benefits. Considering that over 70 % of Indian adults already lack sufficient calcium, an RO system could inadvertently worsen the deficiency.

Dr. Anshuman Kaushal, a gastroenterology specialist and science communicator, reminds us that the WHO’s 2005 rolling revision warned that long‑term consumption of demineralised water may be linked to higher risks of cardiovascular disease, bone loss and hypertension. While most of our minerals should come from food, relying on ultra‑pure water for years can be a hidden problem, especially for those on low‑nutrient diets.

Beyond health, the taste suffers – water that’s been stripped of its natural salts feels flat. And the environmental cost is hard to ignore. A typical RO unit sends about three‑quarters of the incoming water down the drain as waste; for every litre you drink, roughly 750 ml is discarded.

In 2019, the National Green Tribunal ordered the Environment Ministry to ban RO installations where TDS is below 500 mg/L unless the system can recover at least 60 % of the water. Though standards have been drafted by the Bureau of Indian Standards, enforcement remains patchy. Manufacturers, regulators and municipalities all share the responsibility to curb waste.

What about the rejected water? It can be repurposed for mopping floors, watering plants or flushing toilets, yet only a handful of households actually do this.

Should you consider UV or UF instead? The answer hinges on your source. If you receive municipal or piped water with low TDS (under 300 ppm) but there’s a chance of microbial contamination, a UV purifier works well – it neutralises bacteria and viruses without affecting dissolved minerals.

Ultrafiltration (UF) is another option for low‑TDS water that might still harbour microbes. UF membranes block bacteria, viruses and suspended particles, and because they don’t need electricity, they’re handy where power cuts are frequent.

Some homes use a hybrid of RO, UV and UF, but that’s only justified when water is both high in TDS and microbiologically unsafe – think of a borewell that’s mixed with municipal supply, a common setup in semi‑urban areas. For clean municipal water, a single‑stage UV or UF unit usually suffices.

Bottom line? Don’t buy a purifier on impulse. Test your water first. A cheap TDS meter and a one‑time laboratory test for microbes will tell you more than any brand slogan. Once you know the numbers, you can pick the system that truly matches your needs.