Phase 1
Design and Qualification
1Define water grade requirements by use point
Map every use point to its required water grade based on the product or process it supports. Parenteral manufacturing and final equipment rinse require WFI; most other uses can be satisfied by PW.
USP <1231> · ICH Q7 Section 4.3
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2Design generation, storage, and distribution
System design minimizes dead legs, uses continuously circulating loops, and includes appropriate sanitization access points. Storage tanks include hydrophobic vent filters and spray ball distribution.
USP <1231> · EU GMP Annex 1 2022
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3Select sanitization strategy
Thermal sanitization, ozone, or chemical sanitization selected based on system design and materials of construction. Sanitization frequency and efficacy verification method defined before qualification begins.
USP <1231>
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4Execute three-phase qualification
Phase 1: two to four weeks of intensive daily sampling at every use point. Phase 2: additional two to four weeks confirming consistent performance. Phase 3: one year of routine sampling covering seasonal variation.
FDA Guide to Inspections of High Purity Water Systems
Phase 2
Sampling and Testing
5Sample every use point on a rotating schedule
All use points sampled at a defined frequency, with critical use points such as WFI outlets to parenteral filling sampled more frequently than lower-risk points.
USP <1231>
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6Conduct chemical testing
Conductivity tested per USP <645> three-stage methodology, either online or offline. Total organic carbon tested to detect organic contamination not captured by conductivity alone.
USP <645> · USP <643>
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7Conduct microbial and endotoxin testing
Bioburden testing performed per USP <1231> methodology. WFI additionally tested for bacterial endotoxin using the limulus amebocyte lysate method or an equivalent validated method.
USP <1231> · USP <85>
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Do results fall within alert and action limits at every use point?
YES → Record and trend
NO → Investigate excursion
Phase 3
Trending and Review
8Trend chemical and microbial data by use point
Each use point trended independently over time. A result consistently near the alert limit at one location is a signal even while every individual result remains compliant.
USP <1231>
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9Seasonal and long-term pattern review
Phase 3 qualification and ongoing monitoring together capture seasonal variation in feedwater quality. Trends correlated against ambient temperature, feedwater source changes, and system age.
FDA Guide to Inspections of High Purity Water Systems
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10Periodic system performance review
Water system performance reviewed as part of APQR and management review, summarizing excursion rate, trending observations, and any changes made during the review period.
ICH Q10 Section 3.2.1
Phase 4
Maintenance and Recertification
11Scheduled sanitization
System sanitized at a defined frequency using the qualified method. Post-sanitization sampling confirms effective microbial reduction before the system returns to routine use.
USP <1231>
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12Preventive maintenance programme
Pre-filters, RO membranes, ion exchange resin, UV lamps, and other consumable components replaced on a defined preventive schedule tied to manufacturer specification and system performance data.
21 CFR 211.68
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13Trigger-based requalification
Requalification triggered by system modification, sanitization method change, repeated excursions at the same location, or extended system shutdown. Scope determined by risk assessment of the change.
EU GMP Annex 15 · Change control procedure
Alert and Action Limits (USP <1231>)
Conductivity - Stage 1 (USP <645>)
Water passes if conductivity at the measured temperature does not exceed the Stage 1 limit. Stage 1 failure requires progression to Stage 2 and, if needed, Stage 3 with temperature compensation and pH adjustment.
USP <645> Table 1
Purified Water - Microbial Action Limit
Action limit of 100 CFU/mL. This is a level that should trigger investigation, not a specification that may routinely be approached.
USP <1231>
WFI - Microbial and Endotoxin Action Limits
Bioburden action limit of 10 CFU/100mL. Endotoxin limit of 0.25 EU/mL. Both reflect the higher risk profile of water used for parenteral products.
USP <1231> · USP <85>
Excursion Response Steps
Step 1 - Confirm result validity
Rule out sampling technique error, container contamination, or analytical error before concluding a genuine system excursion.
Step 2 - Assess impact on product and downstream use
Identify every batch and process step that used water from the affected use point since the last satisfactory result.
Step 3 - Resample the affected location and adjacent points
Confirm whether the excursion is isolated to one use point or reflects a broader system issue by sampling nearby locations and the return loop.
Step 4 - Investigate root cause
Review recent sanitization records, maintenance activity, filter and membrane age, and any recent system modifications.
Step 5 - Remediate and verify
Sanitize or repair as indicated by the investigation. Confirm return to control with successive satisfactory results before closing the investigation.
Sampling Requirements
Every use point included
All points where water is drawn for manufacturing or cleaning use are included in the routine sampling plan, not only a representative subset.
First-draw sampling technique
Samples taken as water is actually used, without flushing beforehand, so results reflect the water quality a user point actually delivers.
Return loop and storage tank sampling
Storage tank and return loop sampled to monitor overall system performance independent of individual use point results.
Frequency risk-adjusted
Higher-risk use points, such as those feeding WFI directly to parenteral filling, are sampled more frequently than lower-risk points.