What Is TDS in Drinking Water?

What Is TDS?

Total Dissolved Solids (TDS) refers to the combined content of all inorganic and organic substances dissolved in water. This includes minerals, salts, metals, and organic matter present as molecular, ionized, or micro-granular suspended form.

TDS is measured in parts per million (ppm) or milligrams per litre (mg/L) — they are equivalent units.

What Makes Up TDS?

The major components of TDS in drinking water:

• Calcium (Ca²⁺) — from limestone, soil, and pipes
• Magnesium (Mg²⁺) — from soil and rocks
• Sodium (Na⁺) — from salt and water softening
• Potassium (K⁺) — from soil and fertilizers
• Bicarbonates (HCO₃⁻) — from dissolved CO₂ and minerals
• Chlorides (Cl⁻) — from salt and industrial waste
• Sulphates (SO₄²⁻) — from minerals and industrial discharge
• Nitrates (NO₃⁻) — from fertilizers and sewage

Not all TDS is harmful. Calcium and magnesium are actually beneficial for health — the issue is when TDS is too high or too low, or when it includes toxic components like lead or arsenic.

Sources of TDS in Water

Natural sources:

• Dissolved minerals from rocks and soil
• Decaying organic matter
• Natural salt deposits

Human-caused sources:

• Agricultural runoff (fertilizers, pesticides)
• Industrial discharge
• Sewage and wastewater
• Urban runoff
• Old plumbing (metals leaching into water)

How TDS Is Measured

TDS meter: An electronic device that measures the electrical conductivity of water and converts it to a TDS reading. These cost ₹300–₹2000 and give instant results.

Gravimetric method: The laboratory method where water is evaporated and the residue is weighed. This is more accurate but takes time.

Accuracy note: TDS meters measure conductivity and estimate TDS using a conversion factor. They detect dissolved salts and minerals but do not identify individual components. They also cannot detect bacteria, viruses, or pesticides.

Why TDS Matters

• Taste: Low TDS (below 100 ppm) tastes flat. High TDS (above 500 ppm) tastes salty or metallic. Most people prefer 150–300 ppm
• Health: Very high TDS (above 2000 ppm) may cause gastrointestinal issues. Very low TDS (below 50 ppm) lacks beneficial minerals
• Appliance damage: High TDS causes scaling in kettles, geysers, and pipes
• Purifier selection: TDS level determines whether you need RO (above 300 ppm) or can use UV/UF (below 300 ppm)

TDS in Indian Cities

City	Typical TDS Range
Mumbai	100–250 ppm
Kolkata	150–250 ppm
Chennai	200–400 ppm
Delhi	300–800 ppm
Bangalore	300–600 ppm
Hyderabad	400–800 ppm
Jaipur	500–1000 ppm
Ahmedabad	400–700 ppm
Punjab (rural)	500–1500 ppm
Rajasthan (rural)	1000–3000+ ppm

Key Takeaways

• TDS measures all dissolved minerals and salts in water, measured in ppm
• TDS comes from both natural mineral sources and human activities
• Not all TDS is harmful — calcium and magnesium are beneficial
• TDS below 300 ppm usually allows UV/UF filtration; above 300 ppm typically requires RO
• Use a TDS meter for a quick reading, but get lab testing to identify specific contaminants