Ok, I did not want to be the one to start this, but, what the heck, here goes.
ALL diesel fuel, and gas, has trash in it, all of it has some water in it. I had to deal with 90,000 gallons of fuel for the generators I've mentioned above. Naturally, we had water/fuel separators on them, and the filtration system was huge in each machine. My pickup truck has a water separator.
It is not a good thing for significant amounts of water to slip past. If you are reasonably observant, the condensate in your tank will not harm your engine. I still have, and use, water paste to check it about twice a year, I'd do it more often if it were used daily, but then I would have already replaced the CRUMMY fuel filter system Kubota put on the BX-25, and still may one day soon.
Water rides on TOP of the tank, so don't let your tank get low is one tactic, so now you're dealing mostly with the trash one finds in fuel.
The Wix fuel filter prevents anything 50 microns, or larger, from entering the stream. I'm willing to hazard a guess that 50 microns is also the level of filtration on the Kubota filter since that is one fine level of filtration. I don't have my books anymore though, so am hampered there.
It has been proven to me, several times, that the paper element in the Kubota filter will totally plug with a half eye dropper of water in freezing weather, leaving you laying in the snow trying to change a filter! Now, understand, this half eye dropper of fuel doesn't slug all at once, but is cumulative.
The most fun was the first time the front filter stopped me dead in my tracks (the only time) I went and got the book and read 'How to change the front fuel filter' which starts out, use the loader to raise the front end so you can get the hood off! Well, that would be great IF the dam#^% thing would run!
I am using the Wix fuel filters happily, BECAUSE they don't have the paper element in them. 2 years, no hazard, white smoke, or exploding engine, and willing to bet mine will be around as long as anyone's.
Change them annually, because diesel fuel is trashy stuff, even if you're very careful where you buy it.
Probably will upgrade to a for really, real filter system one day, but as it has been said before, that is something Kubota should have done instead of sticking us with lawnmower filters! My one and only complaint with this machine.
George