Overview. Conductivity provides a rapid, non-specific measure of ionic contamination in pharmaceutical water. It is widely used to monitor generation and distribution systems, but reliable interpretation requires understanding of temperature, sensor installation and the limits of what conductivity can demonstrate.
What conductivity measures
Dissolved ions allow water to conduct electrical current. Increased conductivity may indicate salts, cleaning residues, treatment failure or ingress. It does not directly measure organic compounds or microorganisms.
Temperature dependence
Conductivity changes significantly with temperature. Pharmacopoeial approaches define how results are evaluated, and uncritical use of automatic temperature compensation can produce incorrect conclusions.
Online sensor installation
Sensor location, flow, orientation, air bubbles and stagnant conditions affect readings. Online instruments should be installed where they represent system performance and can be maintained safely.
Calibration and verification
Cells require calibration or verification using traceable standards and appropriate procedures. Cell constant, fouling and electronic drift should be considered.
Alert and action limits
Compendial limits define compliance, while internal limits may reflect normal system performance. Sudden or gradual shifts require investigation even when the formal limit is not exceeded.
Integration with water-system control
Conductivity should be reviewed together with TOC, microbiology, pressure, temperature, sanitisation and maintenance. A satisfactory conductivity result cannot compensate for poor microbial control.
Practical reference table
| Influence | Potential effect | Control |
|---|---|---|
| Temperature | Changes measured conductivity | Compendial evaluation approach |
| Air bubbles | Erratic or low reading | Correct orientation and flow |
| Sensor fouling | Drift or slow response | Inspection and cleaning |
| Stagnation | Non-representative result | Suitable flow-through installation |
| Calibration error | Biased reading | Traceable verification |
Control and decision path
Frequently asked questions
What does conductivity tell us?
It provides an indirect measure of ionic contamination.
Can conductivity detect microorganisms?
No. Microbiological testing is separate.
Why is temperature important?
Water conductivity changes with temperature and must be interpreted correctly.
Should online sensors be calibrated?
Yes. Calibration or verification should be defined and documented.
What causes a sudden conductivity increase?
Treatment failure, chemical ingress, cleaning residue, sensor problems or sampling error.
Primary references and guidance
- European Pharmacopoeia 2.2.38, Conductivity
- USP <645>
- EU GMP Annex 1
- EU GMP Part I, Chapter 3
- ISPE Water and Steam Systems Guide
- WHO water-system guidance
- ISO 17025
Confirm the current effective revision and national applicability before operational or regulatory use.