What is TDS in Water? Safe Levels, Indore's Water Quality & How to Test It
You've probably seen the term TDS printed on your RO purifier's display, or heard a technician mention it during a service visit. But what exactly does TDS mean, what number should you aim for, and why does it matter so much in a city like Indore? This guide answers all of that in plain language.
TDS Full Form – What Does It Stand For?
TDS stands for Total Dissolved Solids. It measures the combined total of all substances dissolved in water — including minerals, salts, metals, chloride, sulfate, bicarbonate, and organic matter. It is expressed in milligrams per litre (mg/L), which is equivalent to parts per million (ppm).
When you fill a glass of water from your tap, it looks clear — but dissolved within it are potentially hundreds of substances you can't see. TDS is the number that represents the total weight of all of those dissolved particles in one litre of that water.
📏 How TDS is Measured
TDS is measured using a TDS meter (also called a TDS pen) — a small handheld device that measures the electrical conductivity of water. Since dissolved minerals carry electrical charge, a higher TDS means higher conductivity. A basic TDS meter costs ₹150–₹300 online and gives you an instant reading in mg/L.
What Makes Up the TDS in Water?
Not everything dissolved in water is harmful — some minerals are actually beneficial. TDS includes:
- Natural minerals — Calcium, magnesium, potassium, sodium (mostly harmless or beneficial in small amounts)
- Heavy metals — Lead, arsenic, chromium, cadmium, nitrates (harmful above trace levels)
- Chlorine and chloramines — Added by municipalities to kill bacteria, but undesirable in drinking water
- Fluoride — Added to some water supplies; harmful in large amounts
- Pesticides and industrial pollutants — Can enter groundwater through agricultural runoff
- Organic matter — Decayed plant or animal material
A high TDS doesn't automatically mean the water is dangerous (it could be mostly calcium and magnesium), but it does mean there are more dissolved substances — and the only way to know which ones are present is through a detailed lab test. This is why general TDS limits exist as a practical safeguard.
What is a Safe TDS Level for Drinking Water?
| TDS Level (mg/L) | Rating / Suitability |
|---|---|
| Below 50 | ⚠ Too low — may lack essential minerals |
| 50 – 150 | ✅ Ideal — pure, with balanced minerals |
| 150 – 300 | ✅ Good — acceptable for drinking |
| 300 – 500 | ⚠ Fair — WHO borderline; taste may be affected |
| 500 – 900 | ❌ Poor — BIS upper limit is 500; avoid if possible |
| Above 900 | ❌ Unsafe — not suitable for drinking |
WHO recommendation: Below 300 mg/L. | BIS (India) standard: Below 500 mg/L (upper limit 2000 if no alternative).
A good RO purifier in proper working condition typically produces water with a TDS of 20–80 mg/L — comfortably within the ideal range.
⚠ Is Very Low TDS (Below 50) Also a Problem?
Yes. Water that is excessively pure (TDS below 50 mg/L) lacks essential minerals like calcium and magnesium. Drinking only ultra-pure water long-term can cause mineral deficiencies. This is why quality RO purifiers include a TDS controller or mineraliser that adds back some beneficial minerals after filtration. The ideal output TDS for RO water is 50–150 mg/L.
What is the TDS of Indore's Tap Water?
Indore's municipal water supply draws from the Narmada river and from local groundwater. The TDS varies significantly by area and season:
| Area in Indore | Typical TDS Range | Assessment |
|---|---|---|
| Central areas (Palasia, Vijay Nagar, Rajwada) | 300 – 450 mg/L | Fair — RO strongly recommended |
| Rajendra Nagar, Scheme 54, Annapurna | 350 – 550 mg/L | Poor — RO essential |
| Rau, Mhow, Sanwer Road | 500 – 700 mg/L | High — RO mandatory |
| Khajrana, Sudama Nagar, Bengali Square | 350 – 500 mg/L | Fair to Poor — RO recommended |
These ranges mean that almost no area of Indore has tap water that is safe to drink without purification. Narmada water is somewhat better in quality than groundwater, but both exceed safe TDS limits for direct consumption.
How Does High TDS Affect Your Health?
Regularly drinking water with a high TDS — especially one that is high in heavy metals, nitrates, or fluoride — has been linked to:
- Kidney stones and urinary tract issues (excess calcium, oxalate)
- Gastrointestinal problems — nausea, diarrhoea
- Cardiovascular strain (excess sodium)
- Dental fluorosis in children (excess fluoride)
- Developmental issues in infants from lead or arsenic exposure
Even if your current TDS is at 400 mg/L (BIS acceptable), long-term consumption can have cumulative health effects — particularly for young children, pregnant women, and the elderly.
How Does a RO Purifier Reduce TDS?
A Reverse Osmosis (RO) membrane forces water through a semi-permeable membrane with pores approximately 0.0001 micron in size — small enough to block dissolved salts, heavy metals, and most contaminants, while allowing water molecules through. A quality RO membrane removes 90–99% of dissolved solids, bringing water from 500 mg/L down to 20–50 mg/L.
✅ Quick TDS Test You Can Do at Home
Buy a TDS meter (₹150–₹300). Test your tap water first — that's your baseline. Then test your RO purified water. If the purified water reads below 100 mg/L, your RO is working well. If it reads above 150 mg/L, your membrane may need replacement. Test every 3 months.
When Should High TDS Make You Worry?
- If your RO's output water has climbed above 100 mg/L — the membrane is failing
- If your tap water suddenly tastes saltier or more bitter — TDS may have spiked
- If you notice limescale buildup on taps and utensils — classic sign of high mineral TDS
- If your water has been unserviced for 12+ months — get a TDS check done