Entrained water can stay suspended in turbine fuel for a long time, especially after fueling. This, despite what you think you saw in the mason jar.

When was the last time any of us in a 747 or 737 walked around the airplane with a little plastic cup, sumping something? Never?

If one has never had a fuel drain stick open and refuse to close, one hasn't been flying or sumping very long, and doesn't understand the construction of the drain valve very well. It's very possible for a drain to stick open and not close at all. This, despite the "expert" pilot who keeps stabbing it with his Jr. Fuel Tester.

Checking fuel is a pilot job, not a mechanic job. A turbine airplane is not the same as a piston airplane, however, and if you're carrying your piston habits and know-all with you, you may yet have a few things to learn.