This is a ready-to-use design-review checklist for a pharmaceutical water distribution loop, the part of the system where most inspection findings actually originate. Use it at design qualification or enhanced design review, before fabrication where possible, to confirm the loop can be circulated, drained, and sanitized without harbouring biofilm. Replace every <<FILL: ...>> placeholder, mark each item Pass / Fail / NA with evidence, and route the completed review through QA and Engineering. A filled specimen follows. Verify each cited chapter and guide against the current source. This is general guidance to adapt, not legal or regulatory advice.
How to use
Each item is a design attribute with a pass condition drawn from the recognized engineering practice for high-purity water loops. A Fail is a design change to make before fabrication, or a documented, risk-assessed justification if the design cannot meet it. Numeric targets below are common industry values; confirm the exact figures against your own design basis and the current guides.
Review header
| Field | Entry |
|---|---|
| System / loop ID | <<FILL: system ID, PW or WFI>> |
| Drawing / P&ID reference | <<FILL: drawing no, rev>> |
| Reviewer(s) | <<FILL: names, roles>> |
| Date | <<FILL: date>> |
The checklist
| # | Design attribute | Pass condition | Result (P/F/NA) | Evidence / note |
|---|---|---|---|---|
| 1 | Continuous circulation | Loop recirculates constantly; no fill-and-hold tank in the distribution path | <<FILL>> | <<FILL>> |
| 2 | Turbulent flow | Velocity gives turbulent flow (commonly a target around 1 to 1.5 m/s, Reynolds well into the turbulent regime) at design draw | <<FILL>> | <<FILL>> |
| 3 | Dead legs | Unused branch length to diameter (L/D) below the design limit (commonly less than 6 from the loop inner wall); zero-dead-leg valves preferred | <<FILL>> | <<FILL>> |
| 4 | Slope and drainability | Lines slope to drain; no low pockets that hold water; loop can be fully emptied | <<FILL>> | <<FILL>> |
| 5 | Materials and finish | 316L stainless (or qualified polymer) with controlled interior finish (e.g. Ra below the design value); passivation planned | <<FILL>> | <<FILL>> |
| 6 | Welds | Orbital welds with documented weld map and boroscope inspection; sanitary connections | <<FILL>> | <<FILL>> |
| 7 | Point-of-use valves | Sanitary diaphragm valves and drops that drain and do not create their own dead leg | <<FILL>> | <<FILL>> |
| 8 | Storage tank | Spray ball wets the headspace; hydrophobic vent filter (heated where needed); overlay/gas as designed | <<FILL>> | <<FILL>> |
| 9 | Sanitization coverage | Chosen method (hot circulation, periodic hot water, ozone, steam) can reach every point including the most distal / slowest to heat | <<FILL>> | <<FILL>> |
| 10 | Sample points | Sample valves at every point of use, designed to drain and sanitize, matching how water is used | <<FILL>> | <<FILL>> |
| 11 | Instrumentation | Online conductivity, TOC, temperature (and ozone where used) at generation outlet and return; sanitary pockets that drain | <<FILL>> | <<FILL>> |
| 12 | Data integrity | The PLC/SCADA historian for these signals has audit trail, access control, and synchronized time | <<FILL>> | <<FILL>> |
Decision
| Field | Entry |
|---|---|
| All items Pass or Fail-with-approved-justification? | <<FILL: Yes / No>> |
| Design changes required before fabrication | <<FILL: list or none>> |
| Review outcome | <<FILL: Approved / Approved with actions / Not approved>> |
| QA / Engineering approval (name, date) | <<FILL>> |
References
USP <1231> Water for Pharmaceutical Purposes (loop design, dead legs, sanitization, biofilm). FDA Guide to Inspections of High Purity Water Systems. ISPE Baseline Guide Volume 4 (Water and Steam Systems); ASTM E2500. EU GMP Annex 1 (2022) contamination control strategy.
Confirm the current version of each reference before issue; the numeric targets above are common industry values to verify against your design basis.
Filled specimen
Illustrative extract for a new WFI loop review.
| # | Design attribute | Result | Evidence / note |
|---|---|---|---|
| 2 | Turbulent flow | Pass | Hydraulic calc shows 1.3 m/s at full draw, Re in turbulent regime |
| 3 | Dead legs | Fail | POU-05 drop L/D calculated at 8; redesign to zero-dead-leg valve issued as action DR-04 before fabrication |
| 8 | Storage tank | Pass | Spray ball and heated hydrophobic vent filter on the tank spec |
| 9 | Sanitization coverage | Pass | Hot-water sanitization models 80 C hold at the most distal point; to be confirmed by loop mapping in OQ |
Here the one Fail, a POU drop with an L/D above the limit, is caught at design review and fixed before any pipe is welded, which is far cheaper than finding it as a recurring microbial excursion after start-up.
Common inspection findings this checklist prevents
- Dead legs, oversized drops, instrument tees, and abandoned-in-place lines that hold water.
- A loop that cannot be fully drained, or a thermal sanitization that never reaches the most distal point.
- Storage tank vent filters not heated, so they wet and admit organisms.
- Online water-quality data with no audit trail or access control.
How to adapt this checklist
- Set the loop, drawing reference, and reviewers.
- Replace the common numeric targets with your own verified design-basis values.
- Add items for design-specific features (ozone destruct units, sub-loops, ambient POU coolers).
- Track each Fail as a design action closed before fabrication.
- Confirm every reference against the current published version before issue.