If your TDS meter reads below 200 ppm, congratulations — you have better source water than most Indian households. But does that mean you can skip RO and save money with a UV purifier? The honest answer is: probably yes, but not always. TDS is only one piece of the water quality puzzle, and this guide helps you decide based on the full picture.
What TDS below 200 actually means
TDS (total dissolved solids) measures the combined weight of all dissolved minerals, salts, and metals in your water, expressed in parts per million. A reading below 200 ppm means the dissolved solid content is well within the BIS 10500 desirable limit of 300 ppm. The minerals present at this level — typically calcium, magnesium, sodium, and bicarbonates — are generally beneficial for health.
However, TDS does not measure:
- Bacteria and viruses — a TDS meter cannot detect biological contamination
- Pesticides — even trace amounts do not significantly affect TDS readings
- Heavy metals at low concentrations — 10 ppb of arsenic (above the WHO safety limit) adds negligibly to TDS
- Pharmaceutical residues — not detectable via TDS
- Microplastics — suspended, not dissolved
So low TDS tells you the dissolved salt content is fine, but says nothing about whether the water is actually safe to drink.
Decision framework: do you need RO?
| Your Water Source | TDS Below 200 ppm | Recommendation |
|---|---|---|
| Municipal treated water, modern pipes | Yes | UV + UF is likely sufficient |
| Municipal water, old building (>20 years) | Yes | Get heavy metal test first; RO if lead/iron elevated |
| Borewell water | Yes | RO recommended — test for arsenic, fluoride |
| Mixed supply (municipal + tanker) | Variable | RO + UV — tanker quality is unpredictable |
| Near industrial area | Yes | RO recommended — chemical contamination risk |
| Agricultural area | Yes | RO recommended — pesticide residue risk |
The honest case for skipping RO
If your water meets all these criteria, you genuinely do not need RO:
- TDS consistently below 200 ppm (test in both summer and monsoon)
- Municipal corporation treated water as the sole source
- Modern plumbing (no lead or galvanised iron pipes)
- Lab test confirms no heavy metals, pesticides, or chemicals above BIS limits
- No industrial or agricultural contamination risk in your area
In this scenario, a UV + UF purifier at ₹5,000–10,000 with annual maintenance of ₹1,000–2,500 is the cost-effective choice. You save on purchase price, maintenance, and water wastage.
The honest case for choosing RO anyway
Many families in low-TDS areas still choose RO for good reasons:
- Insurance against variability: Municipal supply quality changes seasonally and during infrastructure work
- Unknown pipe condition: Most Indians do not know the pipe material in their building
- Tanker backup: If you occasionally receive tanker water during shortages, a UV-only purifier cannot handle the TDS spike
- Moving plans: If you may move to a different city or locality, an RO purifier works everywhere
- Peace of mind: RO removes everything UV removes plus dissolved contaminants, providing comprehensive protection
A premium RO purifier with mineral enhancement gives you the safety of complete filtration while restoring the beneficial minerals, effectively giving you the best water quality regardless of what your source throws at it.
How to test your water properly
Level 1: TDS meter (₹200–500, instant)
Tells you dissolved solid content. Test in summer and monsoon for seasonal variation. If TDS is above 300, you need RO — stop here.
Level 2: Full lab test (₹1,500–3,000, 3–7 days)
BIS-accredited labs test for 15–30 parameters including heavy metals, pesticides, bacteria, hardness, pH, fluoride, and nitrates. This tells you definitively whether UV alone is safe. Contact your nearest BIS-accredited lab or check the FSSAI water testing portal.
Level 3: Real-time monitoring (continuous)
Smart purifiers like the Boon Tap with WaterAI monitor your input and output TDS continuously via an app, catching any sudden changes that a one-time test would miss. This is particularly valuable if your water source is variable.
Frequently Asked Questions
Is RO necessary if my water TDS is below 200 ppm?
In most cases, no. If your water TDS is consistently below 200 ppm and comes from a treated municipal source, a UV plus UF water purifier is usually sufficient for safe drinking water. The BIS 10500 standard for Indian drinking water sets the desirable TDS limit at 300 ppm and the permissible limit at 500 ppm. Water at 200 ppm is well within safe dissolved solids range, meaning the minerals present are not harmful and may actually be beneficial for health. However, TDS alone does not tell the complete story. Low TDS water can still contain pesticide residues, pharmaceutical traces, heavy metals from old pipes, or industrial chemicals that a TDS meter cannot detect. If your water comes from a borewell even with low TDS, or if there is industrial activity or agricultural runoff in your area, an RO purifier adds a necessary safety layer that UV cannot provide. The honest answer depends on what is dissolved in your water, not just how much.
What contaminants can UV not remove from low TDS water?
UV sterilisation kills bacteria, viruses, and protozoa by destroying their DNA, but it does not remove any dissolved substances from water. Even in low TDS water below 200 ppm, UV cannot remove dissolved lead from old plumbing pipes, arsenic that occurs naturally in groundwater in parts of West Bengal and Bihar, fluoride that exceeds the safe limit of 1.5 milligrams per litre in several Indian states, pesticide residues from agricultural runoff common in rural and semi-urban areas, pharmaceutical traces from inadequate sewage treatment, chlorine and chloramine disinfection byproducts from municipal treatment, and microplastics that are increasingly found in tap water globally. A comprehensive water test from a BIS-accredited laboratory costs 1,500 to 3,000 rupees and tests for 15 to 30 specific contaminants beyond TDS. This one-time investment tells you definitively whether UV alone is safe for your specific water source or whether you need RO filtration.
Does RO remove beneficial minerals from low TDS water?
Yes, RO removes both harmful and beneficial dissolved minerals, which is why using RO on already-low TDS water raises a valid concern. If your input water is 150 ppm TDS with a healthy calcium and magnesium balance, RO will reduce it to 20 to 40 ppm, stripping out minerals your body benefits from. The WHO notes that very low mineral water below 50 ppm TDS may not provide adequate dietary mineral supplementation, though most nutritional minerals come from food rather than water. This is why premium RO purifiers include a post-RO mineral enhancement stage that adds calcium and magnesium back to optimal levels, typically bringing output TDS to 50 to 80 ppm with a balanced mineral profile. If you choose an RO purifier for low TDS water, ensure it has mineral enhancement as a standard stage rather than an optional add-on. Without it, you get demineralised water that tastes flat and provides no mineral value from your daily 2 to 3 litres of drinking water.
How do I test if my water needs RO or just UV?
Start with a TDS meter test, which costs 200 to 500 rupees for a handheld device and gives instant results. If TDS is above 300 ppm, you need RO. If TDS is below 200 ppm, do a second level of testing. Get a comprehensive water quality report from a BIS-accredited laboratory, which tests for heavy metals, pesticides, bacteria, hardness, pH, and specific contaminants that a TDS meter cannot detect. This costs 1,500 to 3,000 rupees and takes 3 to 7 days. Your municipal water authority may also publish annual water quality reports that you can request under RTI. If the lab report shows all parameters within BIS 10500 limits and your water comes from a reliable municipal source with consistent treatment, UV plus UF is sufficient. If any heavy metal, pesticide, or chemical parameter is elevated, or if your supply includes tanker or borewell water even occasionally, choose RO plus UV for comprehensive protection.
Which Indian cities have low enough TDS for UV-only purifiers?
Very few Indian cities consistently deliver municipal water with TDS below 200 ppm across all areas. Parts of Mumbai receive BMC-treated water from lakes with TDS around 80 to 150 ppm, making UV-only viable in many Mumbai localities. Shimla and several Himalayan hill stations have naturally low TDS spring water. Select areas of Bengaluru served by Cauvery water through BWSSB have TDS around 120 to 180 ppm. Parts of Pune with Khadakwasla dam water and some areas of Kolkata with treated Hooghly river water can fall below 200 ppm. However, even within these cities, TDS varies dramatically by locality, building age, storage tank condition, and season. A building in south Mumbai might get 100 ppm water while another 5 kilometres away gets 350 ppm from a different distribution line. Always test your specific tap water rather than relying on city-level averages. Monsoon season typically dilutes TDS while summer concentrates it.