This should help:
http://www.pre-mac.com/PWP_PWP.HTM
And this from the "Jane's" website;
Title
Pre-Mac hand-held personal water purifiers, models SWP, MWP and PWP (United Kingdom)
Section
WATER SUPPLIES
Appearing in
Jane's Military Vehicles and Logistics
Publication date
Jun 24, 2003
Description
Pre-Mac International's personal water purifiers have been designed for military use in consultation with UK MoD (Army) medical authorities. The complete range are NATO codified and can be supplied with carrying pouches and a simple water test kit. The model SWP is ideal for emergency or survival conditions, while the model MWP which has easily changeable cartridges meets the requirements of lightly scaled troops. The model PWP has the greatest capacity of the Pre-Mac hand-held range of personal water purifiers and screws onto the standard NATO and American-style water bottles. All models in the range produce safe drinking water from sources contaminated with high levels of bacteria, virus and parasitic contamination. They are also capable of removing organic matter, improving taste, smell and the general appearance of treated water. In operation they treat water through a filtration and disinfection process. Source water is initially filtered through a pre-filter to remove solid particles and is then passed through an activated charcoal cloth filter to remove further particulate matter and organic contamination. This is followed by the disinfection process using an iodine resin complex. Secondary disinfection takes place in the water bottle during a holding period of two minutes prior to consumption. This residual biocide ensures that the treated water remains free of bacterial, viral and parasitic contamination.
