The current TRS 970 of the WHO also comprises an updated version of the guideline regarding the manufacture and distribution of water for pharmaceutical use as Annex 3. This revised version contains the same chapters. The modifications are rather based on comments to the previous version which were reviewed and implemented by the WHO Expert Committee. For instance, the range of the guideline's scope was narrowed by excluding the processing small amounts of water in pharmacies. Also new is the indication that already the design of a water system is important for avoiding microbiological growth in the system. Before only the sanitisation was mentioned as measure. The authors also emphasise the importance of the appropriate capacity to ensure a sufficient re-circulation. It is also new that the pharmaceutical manufacturer is in responsible of ensuring that the feed water has drinking water quality. If this is not the case he has to take suitable measures in a step prior to the actual treatment to guarantee this quality. Further, the monitoring of the drinking water quality was amended to consider seasonal effects.
With regard to purified water (AP) the revision now mentions the possible treatment components (reverse osmosis and EDI). The amendment states (similar to the USP) that warning limits are supposed to be based on operational experience. In reality there are often fixed warning limits - like the 50% from the limit in the pharmacopoeia.
Concerning (bulk) highly purified water (HPW) and (bulk) WFI the revision comprises the amendment that these are to be protected against contamination and microbial growth. Likewise for the sanitisation was added that the removal of any added substances has to be verified. Besides ozone, hydrogen peroxide and peracetic acid were added in the list.
The chapter on appropriate materials was also extended by one paragraph. Here the guideline indicates that none of the materials used should contain chemicals that are extracted by the water. In the case synthetic materials are used the raw materials are supposed to have at least food grade standard.
There are also changes in the chapter on bio contamination control. The recommended temperature of 70-80 °C for hot stored systems was reduced to > 65 °C for example.
In the chapter qualification it was added that also the quality of the feed water needs to be inspected as part of the validation and that this testing is supposed to be continued as part of the routine monitoring. In the chapter inspection of a water system it was further added that an on-site inspection of the treatment as well as of the distribution system and the sampling points should be part of the inspection.
You can find further information in the new version of the Guideline "WHO good manufacturing practices: water for pharmaceutical use".