The grades and their numbers
Pharmaceutical water is specified by the pharmacopoeias, not by the supplier. The two bulk grades that matter in most facilities:
- Purified Water (PW) — the base grade for non-sterile manufacture, cleaning and formulation. USP limits: conductivity at or below 1.3 µS/cm at 25 °C (the Stage 1 in-line value; the chapter provides staged off-line testing above it) and total organic carbon at 500 µg/L. The commonly applied microbial action level is 100 cfu/ml, from USP's informational chapter on water systems.
- Water for Injection (WFI) — for parenterals and final rinse of product-contact equipment in sterile manufacture. Same conductivity and TOC limits as PW, with a much tighter microbial action level of 10 cfu per 100 ml plus an endotoxin requirement.
A change worth knowing: since April 2017 the European Pharmacopoeia permits WFI production by methods "equivalent to distillation" — reverse osmosis coupled with techniques such as electrodeionisation or ultrafiltration — ending the distillation-only era. The conditions attached are real: the regulator must be notified, and inspectors focus hard on biofilm control and continuous monitoring in membrane-based WFI systems.
Who inspects what in South Africa
SAHPRA's GMP guideline adopts the PIC/S Guide to GMP outright — South Africa was the first African PIC/S member, back in 2007 — so a pharmaceutical water system here is assessed against the same expectations as in Europe. The WHO's current technical guidance, TRS 1033 Annex 3 (2021), is the reference document inspectors and engineers share, and it is unusually concrete for a guidance text.
The standard generation train
Published practice, consistent across WHO guidance and the major system vendors, runs: municipal or borehole feed at drinking-water quality as the minimum starting point, then softening, dechlorination (carbon, sodium bisulphite dosing or UV — chlorine destroys thin-film RO membranes), then reverse osmosis — usually double-pass — polished by continuous electrodeionisation (EDI) to hold conductivity comfortably inside the limit. Distillation remains an option, and for WFI it is still the conservative choice; membrane-based WFI adds ultrafiltration as the endotoxin barrier.
The loop is the system
What separates pharmaceutical water from every other application is that generation is the easy half. WHO TRS 1033 makes recirculating distribution the default — a one-way system requires justification — with turbulent flow evidenced by Reynolds number above 4 000, zero-dead-leg diaphragm valves, drainable pipework at a minimum slope of 1 in 100, 316L stainless steel or PVDF with orbital welds and hygienic clamp joints (threaded joints are not permitted), and sanitisation either thermally above 70 °C or chemically with ozone, hydrogen peroxide or peracetic acid. Notably, filters are not permitted in the distribution loop or at take-off points — quality is designed in, not filtered in at the end.
The old "6D" dead-leg rule has tightened over the years: current industry guidance works to 3D or 2D, and the modern answer is zero-dead-leg valve design rather than a ratio. Stagnant water grows biofilm faster than any monitoring programme can catch — microbial results arrive days after the water has been used — which is why the design assurance matters more than the test schedule.
Rule of thumb
Get three things right and the rest follows: feed water at drinking-water quality with chlorine fully removed before the membranes, generation sized so the loop never stands still, and a distribution design an inspector can walk — welded, sloped, valved for zero dead legs, and sanitisable. A pharmaceutical water project that starts with the loop design rather than the RO skid is usually the one that validates on schedule.