TDS — Total Dissolved Solids — is the single most useful number for understanding your water quality. It tells you how much is dissolved in your water, and combined with what those dissolved things are, helps determine the right purification technology. Here is everything you need to know.
What Is TDS?
TDS measures the total concentration of all dissolved substances in water — minerals, salts, metals, anions, and cations — expressed in parts per million (ppm) or milligrams per litre (mg/L). These numbers are equivalent: 1 ppm = 1 mg/L. TDS does not measure bacteria, viruses, or other biological contaminants — only dissolved chemical substances. Pure distilled water has a TDS of 0. Seawater has TDS of around 35,000 ppm. Himalayan glacial water has TDS of 10–30 ppm. Delhi municipal water averages 300–600 ppm.
How to Measure TDS at Home
A digital TDS meter is available online for Rs 200–500 and measures TDS instantly. Simply dip the probes in a glass of water and the reading appears on the LCD display. For accurate results, let the meter stabilise for 10–15 seconds. Test at similar water temperatures each time (TDS meters are temperature-sensitive — most have temperature compensation but results vary slightly). Test your tap water, your purifier output, and bottled water to compare.
Safe TDS Levels for Drinking Water
WHO Guidelines: WHO recommends TDS below 300 ppm for drinking water, with 1,000 ppm as the absolute maximum. Above 1,200 ppm, water tastes unpleasant to most people. BIS (India) Standards: IS 10500 specifies acceptable TDS for drinking water as below 500 ppm, with a permissible limit of 2,000 ppm where no alternative is available. Optimal TDS for drinking: Research suggests optimal health benefits from water with TDS of 100–300 ppm — high enough to provide mineral benefit, low enough to not burden the kidneys with excess salt processing. Alkin purifiers target output TDS of 150–250 ppm after the mineral cartridge adds back essential calcium and magnesium.
TDS and Health: What the Research Shows
Very High TDS (above 1,000 ppm): Associated with increased cardiovascular disease risk, kidney stone formation (especially calcium oxalate stones in genetically susceptible individuals), and unpleasant taste leading to under-consumption of water. Very Low TDS (below 50 ppm): Associated with electrolyte imbalance with high water consumption, slightly increased risk of fractures in populations drinking very low mineral water over decades, and potential heart muscle function issues linked to magnesium deficiency in some studies.
The sweet spot (100–300 ppm): Provides adequate mineral intake from water to supplement dietary sources, optimal taste that encourages adequate hydration, and kidney function support without excess mineral burden.
TDS vs Water Quality: The Important Distinction
TDS measures total dissolved solids but not what those solids are. Water with TDS of 300 ppm could be safe (if it is calcium and magnesium in good ratios) or dangerous (if it is arsenic, lead, or fluoride at harmful concentrations). High TDS from mining or industrial runoff can be extremely dangerous even at TDS levels that seem acceptable. This is why TDS measurement must be combined with contamination-specific testing for a complete water quality picture.
Reducing TDS: Your Options
If your water TDS is too high: Reverse Osmosis is the most effective TDS reduction method for home use, typically reducing TDS by 95–99%. Distillation also achieves near-zero TDS but is slow, energy-intensive, and impractical for daily household use. Water softeners reduce hardness (calcium/magnesium) but replace them with sodium, so they do not reduce TDS significantly. Alkin RO purifiers are specifically calibrated to deliver output water in the optimal 150–250 ppm range with a mineral cartridge adding back beneficial minerals after RO filtration. View Alkin's purifier range for your specific TDS needs.
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