TDS — total dissolved solids — is the single most-searched water quality metric in India, and for good reason. It determines whether you need an RO purifier, a UV purifier, or both. But most TDS guides give you a number without explaining what that number actually means for your health and your wallet. Here is the complete picture.
What TDS actually measures
TDS is the total concentration of dissolved inorganic salts (calcium, magnesium, sodium, potassium, chlorides, sulphates, bicarbonates) and small amounts of organic matter in your water, measured in parts per million (ppm) or milligrams per litre (mg/L). One ppm equals one milligram per litre.
A TDS meter works by measuring electrical conductivity — dissolved salts conduct electricity, so higher TDS means higher conductivity. The meter converts this conductivity reading to an approximate TDS value.
What TDS does NOT measure: bacteria, viruses, pesticides at low concentrations, pharmaceutical residues, specific heavy metals, or microplastics. A TDS reading of 150 ppm tells you the dissolved mineral load is low, but it says nothing about biological safety or chemical contamination.
Safe TDS levels: what the standards say
| TDS Range (ppm) | BIS 10500 Classification | WHO Assessment | What It Means for You |
|---|---|---|---|
| Below 50 | — | Flat taste, low minerals | Add mineral enhancement; not ideal for long-term drinking |
| 50–150 | Excellent | Excellent | Ideal drinking water range (ICMR recommended) |
| 150–300 | Desirable | Good | Safe; may not need RO if no chemical contamination |
| 300–500 | Acceptable | Fair | RO recommended; taste may be slightly salty |
| 500–1000 | Above limit | Poor | RO required; not fit for direct consumption |
| Above 1000 | Unfit | Unacceptable | RO mandatory; may need pre-treatment |
TDS across major Indian cities
| City | Primary Source | Typical TDS (ppm) | Purifier Needed |
|---|---|---|---|
| Mumbai (BMC areas) | Lakes (Tansa, Vihar, Tulsi) | 80–150 | UV + UF sufficient for most areas |
| Bengaluru (BWSSB) | Cauvery river | 120–200 | UV may suffice; test for specifics |
| Kolkata | Hooghly river (treated) | 200–400 | RO + UV recommended |
| Pune | Khadakwasla dam | 100–250 | UV may suffice; area-dependent |
| Hyderabad | Krishna/Godavari + borewell | 300–800 | RO + UV required |
| Chennai | Reservoirs + borewell + desal | 500–1500 | RO + UV mandatory |
| Delhi | Yamuna + Ganga Canal | 400–1200 | RO + UV mandatory |
| Gurugram | Borewell dominant | 800–1500 | RO + UV mandatory |
| Jaipur | Groundwater | 400–1200 | RO + UV mandatory |
| Ahmedabad | Narmada canal + borewell | 300–800 | RO + UV required |
These are indicative ranges. Your actual TDS depends on your specific supply line, building age, storage tank, and season.
How to test your TDS
Level 1: TDS meter (₹200–500, instant results)
- Buy a handheld TDS meter online
- Fill a clean glass with room-temperature tap water
- Submerge the electrodes to the marked line
- Wait 10–15 seconds for the reading to stabilise
- Record the ppm value
Test your raw tap water, purified water (if you have a purifier), and tank water separately. Test in both summer and monsoon — seasonal variation can be 100–300 ppm.
Level 2: Comprehensive lab test (₹1,500–3,000, 3–7 days)
A BIS-accredited laboratory tests 15–30 parameters including specific heavy metals, pesticides, bacteria, fluoride, nitrates, and hardness. Essential if your TDS is in the borderline 150–300 range and you want to know if UV alone is safe. Read our guide on when UV alone is sufficient.
Level 3: Continuous monitoring (real-time, ongoing)
Smart purifiers with app monitoring show your input and output TDS continuously. The Boon Tap with WaterAI displays live TDS, pH, and filter health on your phone, catching seasonal changes and sudden spikes automatically. This is the only way to monitor TDS without manually testing every day.
TDS and your purifier choice
| Your TDS | Recommended Technology | Boon Model |
|---|---|---|
| Below 200 | UV + UF (test for chemicals first) | — |
| 200–500 | RO + UV | Boon Tap or Homie Tall |
| 500–2000 | RO + UV (high-capacity membrane) | Boon Tap or Homie Tall (2000 ppm rated) |
| Above 2000 | Industrial pre-treatment + RO | Boon Purify Core (commercial) |
Frequently Asked Questions
What is the safe TDS level for drinking water in India?
The Bureau of Indian Standards (BIS) IS 10500:2012 sets the acceptable limit for TDS in drinking water at 500 milligrams per litre (ppm) with a desirable limit of 300 ppm. The World Health Organisation does not set a health-based guideline for TDS but notes that water above 1000 ppm is generally unpalatable and water below 300 ppm is considered excellent in terms of taste. The Indian Council of Medical Research (ICMR) recommends drinking water TDS between 50 and 150 ppm for ideal mineral balance and taste. Water below 50 ppm tastes flat and lacks beneficial minerals like calcium and magnesium. Water between 150 and 300 ppm is acceptable. Water between 300 and 500 ppm is within BIS limits but may taste slightly salty. Water above 500 ppm exceeds BIS desirable limits and an RO purifier is strongly recommended. Water above 1000 ppm requires RO treatment and is unfit for direct consumption.
How do I test TDS of my drinking water at home?
Testing TDS at home is simple and inexpensive using a handheld TDS meter, available online for 200 to 500 rupees. To test accurately, fill a clean glass with the water you want to test and let it reach room temperature because temperature affects TDS readings. Remove the protective cap from the TDS meter, turn it on, and submerge the electrodes into the water up to the maximum immersion line. Wait 10 to 15 seconds for the reading to stabilise. The display shows TDS in parts per million (ppm), which is equivalent to milligrams per litre. For the most useful data, test three sources: your raw tap water before any purification, your purified water after the purifier, and your storage tank water if you use an overhead or underground tank. Test at different times of day and across seasons because municipal supply TDS can vary with source changes and monsoon dilution. A TDS meter measures total dissolved solids but cannot identify specific contaminants like heavy metals or bacteria.
What is the TDS of tap water in major Indian cities?
TDS levels vary significantly across Indian cities based on water source, treatment, and distribution infrastructure. Delhi NCR typically ranges from 400 to 1200 ppm depending on the area, with south Delhi areas receiving Yamuna water at 400 to 600 ppm and Gurugram borewells reaching 800 to 1500 ppm. Mumbai BMC water from lake sources is among the lowest in India at 80 to 150 ppm. Chennai ranges from 500 to 1500 ppm with significant variation between Metrowater areas and borewell-dependent zones. Bengaluru Cauvery water through BWSSB measures 120 to 200 ppm, but borewell water in the city can reach 500 to 1000 ppm. Hyderabad ranges from 300 to 800 ppm. Kolkata Hooghly river water after treatment measures 200 to 400 ppm. Jaipur and Ahmedabad have some of the highest urban TDS at 400 to 1200 ppm from groundwater sources. These are indicative ranges and actual TDS at your tap depends on your specific supply source and building plumbing.
Is low TDS water unhealthy to drink?
Very low TDS water below 50 ppm may not be ideal for long-term drinking according to a 2004 WHO report that raised concerns about demineralised water. The report noted that water very low in minerals could reduce dietary mineral intake, potentially affect metabolism, and may increase the leaching of minerals from food during cooking. However, this concern applies primarily to fully demineralised water near zero TDS, not to typical RO output at 20 to 50 ppm. Most nutritional minerals come from food rather than water, so the health impact of low-TDS water is modest for people with balanced diets. The practical solution is a post-RO mineral enhancement stage that adds calcium and magnesium back to the water, bringing output TDS to 50 to 80 ppm with a healthy mineral profile. This is why premium purifiers include mineralisation as a standard stage. The ideal output TDS for drinking water is 50 to 150 ppm, which balances safety from contaminant removal with healthy mineral content and good taste.
Does TDS tell you everything about water safety?
No, TDS is an important but incomplete indicator of water safety. TDS measures the total concentration of all dissolved inorganic salts and organic matter in water, expressed in parts per million. It tells you how much is dissolved but not what is dissolved. Water with 200 ppm TDS consisting of harmless calcium and magnesium is perfectly safe. Water with 200 ppm TDS that includes 50 parts per billion of arsenic is dangerously contaminated, even though both read the same on a TDS meter. TDS cannot detect bacteria, viruses, pesticides at low concentrations, pharmaceutical residues, or specific heavy metals at harmful levels. For complete water safety assessment, you need a comprehensive laboratory test from a BIS-accredited lab that analyses 15 to 30 specific parameters including heavy metals like lead and arsenic, bacterial contamination, hardness, pH, fluoride, nitrates, and pesticide residues. TDS testing is a useful first screening step that tells you whether RO is needed, but it should not be your only measure of water safety.