TDS Calculator

Determine the total dissolved solids in water using either electrical conductivity (EC) conversion or by summing individual ion concentrations. Get water quality classification and detailed ion breakdown.

Measured electrical conductivity of water

Typically 0.5-0.7 (0.5 for NaCl, 0.64 for natural water, 0.7 for KCl)

Concentration of calcium ions

Concentration of magnesium ions

Concentration of sodium ions

Concentration of potassium ions

Concentration of chloride ions

Concentration of bicarbonate ions

Concentration of sulfate ions

Total Dissolved Solids: Method 1: EC Conversion TDS = k × EC Where: • TDS = Total Dissolved Solids (mg/L) • EC = Electrical Conductivity (µS/cm) • k = Conversion factor (0.5 to 0.7) - 0.50 for NaCl-dominated water - 0.64 for natural mixed-ion water - 0.67 for typical surface water - 0.70 for KCl-dominated water Method 2: Ion Summation TDS = Σ[cations] + Σ[anions] Common ions: Cations: Ca²⁺, Mg²⁺, Na⁺, K⁺ Anions: HCO₃⁻, Cl⁻, SO₄²⁻, NO₃⁻ TDS Classification: • < 50: Very Low • 50-150: Low • 150-300: Moderate (Excellent) • 300-600: Good • 600-900: Fair • 900-1200: Poor • > 1200: Unacceptable
Example 1: EC to TDS Measured EC: 500 µS/cm Conversion factor: 0.64 (natural water) TDS = 0.64 × 500 = 320 mg/L Classification: Good (Fair drinking quality) Example 2: High TDS Water Measured EC: 1450 µS/cm Using k = 0.5 (NaCl dominant) TDS = 0.5 × 1450 = 725 mg/L Classification: Fair - noticeable salty taste Example 3: Ion Analysis Given concentrations (mg/L): Ca²⁺: 40, Mg²⁺: 12, Na⁺: 20, K⁺: 5 HCO₃⁻: 150, Cl⁻: 35, SO₄²⁻: 25 Cations = 40 + 12 + 20 + 5 = 77 mg/L Anions = 150 + 35 + 25 = 210 mg/L TDS = 77 + 210 = 287 mg/L Classification: Moderate (Excellent) Example 4: Pure vs Mineral Water • Distilled water: TDS ≈ 0-5 mg/L • Spring water: TDS ≈ 50-250 mg/L • Tap water: TDS ≈ 150-400 mg/L • Mineral water: TDS ≈ 500-1500 mg/L • Seawater: TDS ≈ 35,000 mg/L Common k Factors by Water Type: • RO/DI water: 0.5 • Freshwater: 0.55-0.65 • Brackish: 0.6-0.7 • Seawater: 0.65-0.7

What is total dissolved solids (TDS)?

TDS measures the combined content of all inorganic and organic substances dissolved in water, including minerals, salts, metals, and ions. It is expressed in mg/L or ppm. Common dissolved solids include calcium, magnesium, sodium, potassium, bicarbonates, chlorides, and sulfates. High TDS can affect water taste, quality, and suitability for various uses.

How is TDS related to electrical conductivity (EC)?

TDS and EC are directly related because dissolved ions conduct electricity. The relationship is TDS = k × EC, where k is a conversion factor typically between 0.5 and 0.7. For pure NaCl solutions, k = 0.5. For natural waters with mixed ions, k = 0.64-0.67 is commonly used. The exact factor depends on the ionic composition of the water.

What are acceptable TDS levels for drinking water?

According to WHO guidelines, excellent drinking water has TDS below 300 mg/L, good water is 300-600 mg/L, fair is 600-900 mg/L, and poor is above 1200 mg/L. The EPA secondary standard recommends TDS below 500 mg/L. Water with TDS above 1000 mg/L often tastes salty or mineralized. Most bottled water has TDS between 50-300 mg/L.

Can I measure TDS directly or do I need to calculate it?

TDS can be measured directly by evaporating a filtered water sample and weighing the residue (gravimetric method), or calculated from electrical conductivity using a conversion factor. The gravimetric method is more accurate but time-consuming. EC meters with TDS conversion are convenient for field measurements. For ion-specific analysis, TDS is calculated by summing all measured ion concentrations.

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