The TDS meter in your kitchen reads 25. The water looks clean and the number is tiny, so it feels like a win. But "lower is better" is not how drinking water works.
Is RO water safe to drink? WHO proposes no health-based limit for TDS. But if your source water is already under 500 mg/L, RO may remove minerals along with the salts. Here is what the standards and studies actually say, and how to decide for your own home.
What is TDS, and what limit does India allow?
TDS means total dissolved solids: the salts and minerals dissolved in water. In India, the BIS drinking water standard (IS 10500:2012) sets an acceptable TDS limit of 500 mg/L and a permissible limit of 2,000 mg/L when no alternate source exists. The same standard says values above the acceptable limit render the water not suitable, but they may be tolerated if there is no alternative source.
WHO looks at TDS mainly as a matter of taste. A WHO background document says tasters rated water as excellent below 300 mg/L, good between 300 and 600, fair between 600 and 900, poor between 900 and 1,200, and unacceptable above 1,200. The same document says water with extremely low TDS may taste flat, and that no health-based guideline value is proposed for TDS.
Is low-TDS RO water bad for your health?
The honest answer is that the evidence is limited, and it points to a possible concern about minerals, not to poisoning.
- Cooking: A paper in the Medical Journal Armed Forces India says cooking with demineralised soft water can cause losses of up to 60% for magnesium and calcium from food. The authors measured RO water at two garrisons at 50 to 180 ppm (average 124), and described it as practically soft water.
- Magnesium in water: A meta-analysis of nine articles found that higher magnesium in drinking water was linked to lower coronary heart disease mortality (relative risk 0.89). Nine of the 10 studies were from Europe, and the results varied a lot between studies.
- Systematic review: A 2024 review of 10 articles found that long-term consumption of demineralised water resulted in lower quality of certain nutrient intake.
These are studies of links, not proof that RO water harms a healthy adult. They are a reason to ask whether you need RO, not a reason to panic.
Do you actually need an RO purifier at home?
It depends on your source water. The NGT's 2019 reasoning, as reported by Down To Earth, was that RO is only meant to treat dissolved solids, and under BIS standards drinking water is considered below par only if TDS is above 500 mg/L. The tribunal directed that the ministry may issue a notification prohibiting RO where TDS is less than 500 mg/L, and that water recovery should be more than 60% wherever RO is permitted.
The legal position is unsettled. In March 2022, Millennium Post reported that the Supreme Court stayed a later NGT order directing the CPCB to bar RO sales where TDS is below 500 mg/L. We could not confirm a later ruling, so do not treat this as a rule for your home. Use it as a hint about when RO adds little.
How can you check your own water?
Do these steps in order.
- Measure your source TDS. A TDS meter gives a quick number. Take the reading before water goes through your purifier.
- Do not stop at TDS. WHO says that where TDS is very high, the individual constituents should be identified, and that guidelines exist for some of them, including boron, fluoride and nitrate. A meter also cannot show germs. Our guide on DIY Water Test Kits: What They Can (And Can't) Actually Detect explains the limits.
- Get a lab test if TDS is above 500 or you are unsure. Ask which contaminants were found, then choose a purifier that matches the problem.
- If your TDS is already low, ask the purifier seller or a lab why RO is needed, and what it is removing.
The NGT petition also argued that indiscriminate use of RO was causing huge wastage of water. For more on India's water risks, read India's 2026 Water Crisis: Over 5,500 Fell Sick. Nobody Talks About It. and Why Ayurveda Calls Plain Water "Dead" — And Science Just Agreed. To see how much water you should drink each day, use the Daily Water Intake Calculator.
What is the ideal TDS for drinking water in India?
BIS accepts up to 500 mg/L. WHO taste panels rated water below 300 mg/L as excellent and 300 to 600 mg/L as good. WHO proposes no health-based value for TDS.
Is 50 ppm TDS water safe to drink?
WHO has no health-based limit for TDS. But very low-mineral water may taste flat, and the studies above raise questions about long-term mineral intake. Safety also depends on germs and chemicals that a TDS meter cannot show.
Does RO water remove calcium and magnesium?
RO removes dissolved solids, which include minerals. A Medical Journal Armed Forces India paper measured RO water at 50 to 180 ppm and described it as practically soft water, devoid of mineral content.
Is RO banned in India?
We found no confirmed nationwide ban. The NGT directed action on low-TDS areas, and the Supreme Court stayed a later NGT direction in 2022. Check the latest position before relying on this.
If you like packaged water with minerals added after purification, Amaayu's Alkaline Water is purified water with calcium, magnesium, potassium and sodium added. It is a packaged drink, not a fix for any mineral gap.
This article is general information, not medical advice. For water quality problems in your area, get your water tested by an accredited laboratory.
