USP <645> - Water Conductivity

What it says

General Chapter <645> describes a staged conductivity testing methodology for pharmaceutical waters, providing a chemical purity indicator based on the water's ability to conduct electrical current, with a three-stage testing approach allowing simpler online measurement to substitute for more complex offline testing when results clearly pass or fail.

Paraphrased for plain-language clarity. Always verify against the current published regulation text.

What it means in practice

• Conductivity testing works alongside total organic carbon testing under Chapter <643> as one of the two primary chemical quality indicators for pharmaceutical water, together substituting for the more extensive chemical testing panels historically required.
• The staged testing approach allows online, continuous conductivity monitoring to serve as the primary control method, with more detailed offline testing reserved for results falling into an intermediate range requiring further evaluation.
• Online conductivity monitoring is widely used precisely because it provides real-time data supporting the kind of continuous system monitoring and trending that pharmaceutical water quality control depends on.

What inspectors look for

• Whether the staged conductivity testing approach is correctly implemented, with appropriate escalation to further testing when initial results fall outside the range for automatic pass determination.
• Whether online conductivity data is genuinely monitored and trended in real time, not simply logged without active review.
• Whether conductivity monitoring equipment itself is properly calibrated and maintained, since conductivity measurement accuracy depends on properly functioning instrumentation.

Related regulations