Does water temperature affect TDS readings?

The Relationship Between Conductivity and Temperature

The electrical conductivity of water is directly influenced by its temperature. This is because ions-the charged particles responsible for conducting electricity in water—move faster at higher temperatures. As their mobility increases, so does the ability of water to conduct electrical current.

Why Temperature Affects Conductivity

As temperature rises, the kinetic energy of the ions increases. This enhanced movement allows ions to carry electrical charge more efficiently, resulting in higher conductivity readings. However, the rate of this increase depends on the specific composition of the water.

General Rate of Change

• Pure water: Conductivity increases by approximately 4.55% per °C (or about 2.5% per °F). This is a fairly linear relationship.

• Sodium chloride (NaCl) solutions: The increase is more moderate, around 2.12% per °C.

• Tap and natural waters: These contain a variety of ions, so the temperature response may vary. While often less pronounced than in pure water, the effect may not always be linear due to the complexity of mixed ion solutions.

Importance of Temperature Compensation

Because of this strong temperature dependency, nearly all modern conductivity meters are equipped with built-in temperature sensors. These allow the instrument to:

• Measure both conductivity and temperature simultaneously

• Apply automatic temperature compensation (ATC) to normalize results, typically referencing 25 °C as a standard temperature

• Improve accuracy when comparing readings across different conditions

Practical Implications

When testing or comparing conductivity values, whether in purified, tap, or process water, temperature must always be taken into account. Ignoring it can lead to incorrect conclusions about water quality, ion concentration or system performance.