TDS vs Conductivity — Understanding the Difference

 TDS vs Conductivity — Understanding the Difference 

PART 2: 

Did you know that TDS and conductivity are related, but they are not the same measurement? Both are important indicators used to monitor water quality and the performance of water-treatment systems.

In Part 2 of our AquaTradeHub Water Treatment Education Series, let’s explore the key differences.

💧 1. What Is TDS?

TDS (Total Dissolved Solids) estimates the concentration of dissolved substances in water, including dissolved salts and other inorganic and organic matter.

📌 Common units: mg/L or ppm

⚡ 2. What Is Conductivity?

Conductivity measures water’s ability to conduct electrical current, primarily due to dissolved ions such as calcium, magnesium, sodium, chloride, and sulfate.

📌 Common units: µS/cm or mS/cm

📊 3. Key Differences

🔹 TDS: Expresses dissolved-solids concentration, usually as an estimated or analytically determined value.

🔹 Conductivity: Indicates how readily water conducts electricity due to dissolved ions.

🔹 Relationship: Conductivity often increases as dissolved ionic content increases, but the relationship depends on the water's chemical composition.

🔄 4. Useful Unit Conversion

✅ 1 mS/cm = 1,000 µS/cm

Remember: this converts conductivity units, not conductivity into TDS.

🧮 5. Estimating TDS

TDS (mg/L) ≈ Conductivity (µS/cm) × TDS Factor

A factor such as 0.65 may be used for an illustrative estimate, but the correct factor depends on the water composition and should be validated for the application.

⚠️ Important Note: Conductivity-based TDS readings are estimates, not universal conversions. For critical water-quality decisions, use an appropriate validated method.

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