There is an adapter that is sold to adapt the Cat filter to be used instead of the OEM filter or it can be used as a final filter with the OEM as prefilter. There has been no reports of any failures or problems with the filters in the year or so that people have been using them on the TDI forum. Some people have had instalation problems, but that has nohing to do with the filter.
What's really nice is the fuel sample testing that has been done on these filter, talking about cleaning dirty fuel.
As far as how much water required to block the filter I have no idea, the filter holds about a pint of fuel so go from there. I did see a filter removed from a TDI at the last GTG at my house that had a few drops of water in the fuel filter when removed. However that was not the problem as it was the dirt & trash in the filter. The car had been running bad since the guy had filled up last before coming to the GTG. The fuel when dumped out of the filter was full of small particiales of crap and what looked like grains of sand and about 3 drops of water. Needless to say we change the filter (OEM) on the car.
Here's a
link to filter adaptor and having both ordered the adaptor from Greg and been to his home and visited with him while he installed new injector kits and pop tested them prior to instaling. He has my vote of confidence.