Pharmaceutical Purified Water Systems: Design, Validation and the Failures We See Most

Note what is not there: no TDS, no hardness, no pH limit. PW compliance is about conductivity, organics and microbiology — and the third is the one that fails. A system can produce 0.5 µS/cm water all day and still be out of specification because the loop grows biofilm.

1. Feed water and pre-treatmentMunicipal or borewell feed → multimedia or UF → softener (or antiscalant) → activated carbon or SMBS dosing for chlorine → 5 µm and 1 µm cartridges. The pre-treatment is sized for the worst feed, not the average, and includes a break tank with UV.
2. Reverse osmosisTwo-pass RO with hot-water-sanitisable membranes; first-pass permeate pH-adjusted with NaOH to convert CO₂ to bicarbonate so the second pass and EDI can remove it. Sanitary design: SS316L, tri-clamp, no dead legs.
3. ElectrodeionisationEDI polishes to < 0.1 µS/cm continuously without regeneration chemicals — the standard for PW. Membrane degassing ahead of it reduces CO₂ load and protects conductivity margin.
4. UV and final filtration254 nm UV for microbial control, 185 nm where TOC is marginal; 0.2 µm sanitary filter before the storage tank.
5. Storage and distributionSS316L tank with spray ball, hydrophobic vent filter and rupture disc; recirculating loop at ≥ 1 m/s (turbulent) with ≤ 6D dead legs, orbital welds, sloped for drainability, ambient loop with periodic hot-water (80 °C) or ozone sanitisation.
6. Instrumentation and dataOnline conductivity with temperature compensation at generation outlet and loop return, online TOC, flow and pressure per loop, 21 CFR Part 11 compliant data logging.

• User Requirement Specification (URS): capacity, quality grade, points of use, sanitisation method, alarm and data requirements.
• Design Qualification (DQ): P&ID review against URS, material certificates, weld maps, slope and dead-leg verification.
• Installation Qualification (IQ): as-built verification, passivation records, instrument calibration certificates, boroscopy of welds.
• Operational Qualification (OQ): every function, alarm and interlock tested; sanitisation cycle proven to reach temperature at the coldest point.
• Performance Qualification (PQ) in three phases: 2–4 weeks daily sampling at every point of use, then 2–4 weeks, then one year covering seasonal feed variation — the system is only released after Phase 3 data supports the sampling plan.
• Ongoing: trending of conductivity, TOC and microbial counts with alert and action limits; change control on any modification.

• Dead legs from later modifications — a valve added for a new machine with 20 cm of stagnant pipe behind it.
• Loop velocity below 1 m/s after points of use were added; biofilm follows within months.
• Cold PW loop sanitised “when counts go up” instead of on a validated schedule.
• Pre-treatment breakthrough: exhausted carbon lets chlorine reach RO membranes, or hardness reaches EDI and scales it.
• Conductivity meters without temperature compensation, or never calibrated against a reference.
• Vent filters that are wet, missing or never integrity-tested — the tank breathes contaminated air.
• No CO₂ management: EDI conductivity drifts up as feed alkalinity varies.

Water for Injection adds an endotoxin limit and a microbial limit a thousand times tighter. Traditionally it is produced by multi-column distillation from PW; the European Pharmacopoeia (since 2017) and others now also accept membrane-based WFI (RO + UF or double-pass RO + EDI with appropriate sanitisation and monitoring). Either way the PW generation and pre-treatment described above is the foundation — a poor PW system cannot feed a compliant WFI system.

URS workshop, feed-water analysis and DQ-ready P&IDs; sanitary fabrication with material traceability; FAT at works and SAT on site; IQ/OQ execution support and PQ sampling plan; operator training and annual requalification support. Capacities from 500 L/h to 50 m³/h. See the high-purity water page for the technology overview.