Water Quality Measurement by Conductivity (Conductometry)

How does conductivity measurement work?

Conductometry measures a solution's ability to conduct electricity. Dissolved ions in water act as charge carriers; as ion concentration increases, so does conductivity. In a contacting sensor, an alternating voltage is applied between two or four electrodes, and conductivity is calculated from the current that flows. A toroidal (inductive) sensor uses two windings that do not touch the sample; one winding induces a current in the liquid loop, and the other measures that current.

Conductivity depends strongly on temperature, so temperature compensation is applied to the measurement. In very pure waters, the result is often also given as resistivity.

What conductometry measures and where it is used

Conductivity is a fast, general indicator of the amount of dissolved ionic matter. Main uses:

• Monitoring demineralized and ultrapure water quality
• Tracking conductivity in boiler water and the steam cycle
• Power plant water-steam control with cation conductivity and degassed cation conductivity
• Monitoring cooling water and reverse osmosis inlet/outlet
• Wastewater and process water control

Cation and degassed cation conductivity

In power plants, the steam sample is first passed through a cation resin column. The resin removes alkaline dosing chemicals such as ammonia and amines, leaving the acids of corrosive anions such as chloride and sulfate. The conductivity of these components is measured more distinctly. In degassed cation conductivity, dissolved CO₂ is also removed, so that conductivity reflects only strong acid anions.

Where conductometry works well and where it struggles

Conductivity measurement is fast and continuous, needs little maintenance and connects easily to control systems. Toroidal sensors resist fouling in high-conductivity and corrosive samples.

Limitations: the method does not say which ions are present; it shows only the total ionic load. The sensor constant and contamination affect measurement quality. In ultrapure water, atmospheric CO₂ ingress can change the result, so a closed flow cell is used.

Choosing an instrument for conductometry

When selecting, the measurement range (ultrapure water, boiler water or high-conductivity process), contacting or toroidal sensor, single or dual channel and temperature compensation features are taken into account. In cation conductivity applications, tracking resin column exhaustion is also part of maintenance.

Tetra and conductivity analyzers

Tetra supplies, installs, commissions, calibrates and services conductivity analyzers and related systems in Türkiye. The product range includes the Thermo Orion 2104CD conductivity analyzer, AV88 and AquaPro (with a conductivity channel), Yokogawa FLXA202, the SENTRY DCCP degassed cation conductivity panel and the SENTRY RC resin column. Tetra also prepares SWAS water-steam analysis systems and pH and conductivity analysis systems.