Micron ratings of filters really annoy me - though they are commonly used in (liquid) filtration. (almost all) Filters are not sieves, so they usually don't remove all of the particles of a given size. So a "5 micron rated" filter will probably only remove ~50% of 5 micron particles.
Water filtration is not really the same as solid contaminant filtration in fluids. The (hydro) -phobicity or -philicity of the media is often just as or more important than the fibre diameter etc (i.e. how well it filters).
Modern (commonrail) engines need better water removal than older engines. Also, all diesel can now have up to 5% bio in AU, with 10% coming soon. This has caused extra issues, as water is (partially) soluble in most bio, and the water can come out of solution after it has passed through the filter.
If I had a puma, I would contact Donaldson or Fleetgard and see what they reccommend as an additional filter.
Failing that, just putting one of the good old CAV filter/sedimenters before the main filter will - at the very least - extend the life of the $$$ main filter, but should also reduce the chance of water getting through. Before anyone says that the CAV won't handle the flow/pressure, there are plenty of prople using them on toyota D4D engines.

