Purified water and WFI system
Water for injections (WFI) · Purified water (PW) · Water treatment plant · Hot WFI loop
The plant that makes pharmaceutical water and the loop that keeps it fit for use at every outlet: generation, storage, circulation, sanitisation and monitoring.
What this page does not claim
An equipment family page teaches how a kind of equipment works and how it is assured. It is not a qualification of any site’s equipment, sets no universal limits, and was checked by SPEQ against the sources it lists, not by an independent engineer.
WHAT IT DOES
A water system makes water to a pharmacopoeial grade and delivers it to points of use without letting microbes, endotoxin or particles in. Annex 1 asks that the plant and its distribution be designed and maintained "to prevent microbiological contamination and to ensure a reliable source of water of an appropriate quality" (6.7), and that the water meet the current monograph of the relevant pharmacopoeia.
Water for injections must be produced by distillation or by a process equivalent to it, which may include reverse osmosis with electrodeionisation, ultrafiltration or nanofiltration. It is stored and distributed to minimise microbial growth, for example "by constant circulation at a temperature above 70°C" (Annex 1, 6.10).
Where it sits: From the utility area to every point of use: formulation, component and equipment washing, final rinses, and the feed to the pure steam generator.
WHERE YOU FIND IT
- Formulation of parenteral products
- Final rinse of product-contact equipment and components
- Feed water for pure steam generators
- Laboratory use where the method requires it
In the reference facility: Clean utilities — WFI, clean steam & process gas, Processing & formulation suite, Equipment wash & parts preparation
Not covered on this page: Potable water and its supply; Water for non-sterile products where a lower grade is justified; The pharmacopoeial limits themselves, which the monographs set.
MAJOR COMPONENTS
- Pretreatment (softening, carbon, filtration). Prepares feed water for the purification step.
- Purification (still, or reverse osmosis with EDI and further steps). Produces the water grade; Annex 1 names distillation or an equivalent process for WFI (6.10).
- Storage tank with vent filter. Holds water; a hydrophobic vent filter is integrity tested before installation and after use and kept free of condensation (Annex 1, 6.11).
- Distribution loop, pump and heat exchangers. Circulates water continuously, hot for WFI, with turbulent flow (Annex 1, 6.9, 6.10).
- Points of use and sampling valves. Deliver and sample water; each outlet is in the sampling programme (Annex 1, 6.13).
- On-line instruments. Conductivity, TOC, temperature and flow, monitored continuously on WFI systems (Annex 1, 6.15).
Connects to: Pure steam generator; CIP systems and washers; Formulation vessels; Laboratory testing; Building management or SCADA system.
INSTRUMENTS AND WHAT THEY MEASURE
- Conductivity sensor. Ionic quality of the water, continuously on WFI systems at risk-based locations (Annex 1, 6.15). Watch for: compensated and uncompensated readings compared as if they were the same.
- Total organic carbon (TOC) analyser. Organic carbon, continuously on WFI systems (Annex 1, 6.15). Watch for: system suitability not shown for the analyser and method.
- Temperature sensor (RTD or thermocouple). Loop and tank temperature, for hot storage and sanitisation. Watch for: sensor not at the location that matters (cold spot, load centre).
- Flow meter. Return flow of the loop, to show turbulent flow is kept (Annex 1, 6.9). Watch for: flow measured at the supply while the low point is at the return.
PARAMETERS
SETPOINT · MEASURED · LIMIT · ATTRIBUTE- Conductivity (attribute, µS/cm). Against the monograph of the relevant pharmacopoeia (Annex 1, 6.7), with on-line monitoring for WFI (6.15).
- Total organic carbon (attribute, ppb C or mg/L C). Against the monograph; on-line for WFI (Annex 1, 6.15).
- Bacterial endotoxin (attribute, EU/mL). Sampled at points of use; part of the release of the system after disinfection (Annex 1, 6.12).
- Microbial count in water (limit, CFU/100 mL or CFU/mL). Alert levels set from the site’s qualification data and reassessed periodically; action limits investigated for root cause and product impact (Annex 1, 6.13, 6.14).
- Temperature (setpoint, °C). Hot circulation of WFI, given by Annex 1 as an example at above 70°C (6.10); the site’s design sets its own.
- Distribution loop flow (measured, m/s or L/min). Established in qualification and routinely monitored so flow stays turbulent (Annex 1, 6.9).
SPEQ publishes no universal alarm or acceptance values: they depend on the process, the product and the site’s own qualification.
CONTROLS, ALARMS AND INTERLOCKS
- Control loop: Loop temperature and flow control. Keeps circulation hot and turbulent.
- Alarm: Conductivity, TOC, temperature or flow out of range. Warns that water quality or the conditions that protect it have moved.
- Procedure: Sanitisation schedule. Sterilisation, disinfection or regeneration on a predetermined schedule and after out-of-limit results, with water tested before return to use (Annex 1, 6.12).
- Procedure: Sampling programme. All outlets and points of use at a specified interval, worst-case locations considered, and at least one representative sample every day of the water used in manufacturing (Annex 1, 6.13).
An alarm asks for a response; an interlock stops an action; a safety function protects people and has its own risk basis.
HOW IT FAILS
- Dead legs or poor drainage. Stagnant water where biofilm forms (Annex 1, 6.7).
- Flow too low to stay turbulent. Microbes adhere and biofilm develops (Annex 1, 6.9).
- Loss of hot circulation. Conditions for microbial growth in WFI.
- Wet or damaged vent filter. The tank draws in contaminated air (Annex 1, 6.11).
- Return to use before results are approved after disinfection. Water of unknown quality used in production (Annex 1, 6.12).
ASSURANCE ACROSS THE LIFECYCLE
EXAMPLES, NOT A MANDATORY LIST- Design. Water grade by use, from the CCS risk assessment (Annex 1, 6.1, 6.2); Drawings with pipe slopes, diameters, valves and user points (Annex 1, 6.5).
- Qualification and validation (Annex 1, 6.8). Physical, chemical and microbial performance; Seasonal variation taken into account; Flow rate established for turbulent flow.
- Routine. On-line conductivity and TOC for WFI; Chemical and microbial sampling to the programme; Trend analysis of critical results (Annex 1, 6.4).
- Excursions. Alert excursions reviewed for isolated event or trend; Action excursions investigated for root cause and product impact (Annex 1, 6.14).
- Sanitisation and change. Sanitisation records and post-sanitisation results; Requalification after changes.
WHAT THIS DOES NOT PROVE
- On-line conductivity and TOC within limits do not prove the water is microbiologically acceptable. Instead: Microbial and endotoxin results from the points of use.
- A good sample from one outlet does not prove every outlet is good. Instead: The sampling programme across all outlets and worst-case locations.
- Hot circulation does not prove there is no biofilm in a dead leg. Instead: Design drawings, drainage, and trend data from the affected outlets.
SOURCES
2 CITED- EU GMP Annex 1: Manufacture of Sterile Medicinal Products — European Commission (EudraLex Volume 4), 2022 revision, in operation 25 August 2023. EU / EEA; revised jointly with the PIC/S Committee; in force. Supports: Utility risk (6.1–6.5); water system design, turbulent flow and WFI production (6.7–6.10); vent filters (6.11); sanitisation (6.12); monitoring, alert and action levels (6.13, 6.14); on-line TOC and conductivity (6.15).
- EU GMP Annex 15: Qualification and Validation — European Commission (EudraLex Volume 4), 2015. EU / EEA; in force. Supports: The qualification and validation approach Annex 1 applies to water systems.
HOW THIS PAGE WAS CHECKED
Researched and checked against the sources above by SPEQ (Claude) on 2026-10-21. It has not been reviewed by an independent engineer. It teaches how this kind of equipment works and is assured; it does not say any site, asset or process is qualified, validated or compliant.
- Pharmacopoeial limits for water grades are not restated; a later revision adds the monographs as sources once checked against the current editions.
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