Water System Validation
Water Conductivity Limit Calculator
Compare a measured conductivity reading against the temperature-based Stage 1 limit from USP <645> / EP for Purified Water and Water for Injection.
How Conductivity Testing Works
USP <645> (and the equivalent Ph. Eur. approach) defines a three-stage conductivity test for Purified Water and Water for Injection. Stage 1 is an online or at-line, non-temperature-compensated measurement compared directly against a temperature-based limit table — if the reading passes Stage 1, no further testing is required.
Why the Limit Changes with Temperature
Conductivity naturally increases with water temperature (higher ion mobility), so the same water sample reads differently at 15°C than at 80°C. Rather than requiring temperature compensation, USP <645> provides a table of acceptable conductivity limits at each temperature increment, allowing a direct online reading to be judged against the correct limit for that temperature.
Total Organic Carbon (TOC)
Alongside conductivity, Purified Water and WFI must also meet a TOC limit — commonly 500 ppb (µg/L) — as a control for organic contamination not detected by conductivity alone.
Interactive Stage 1 Pass/Fail Calculator
USP <645> Stage 1 Reference Table (Approximate)
| Temp (°C) | Limit (µS/cm) |
|---|
Values shown are approximate, commonly cited reference points interpolated between standard table increments, for engineering/educational use. Always confirm against the current official USP <645> table (or Ph. Eur. equivalent) for GMP testing and release decisions — Stage 2 and Stage 3 testing (with pH-adjusted, temperature-compensated measurement) apply if Stage 1 is not met.
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