Is their a good quick way to test for water?
Yes they sell a cream that can be rubbed on the side of a hose or a tank stick , that changes color with water...QUOTE]
It's called water finding paste and any home heating oil company should have it. I'm not sure how much it will help though unless your fill spout is right over the outlet of your fuel tanks. You have to have a measurable water/fuel interface for it to work.
If you have run that far with that fuel, keep switching filters and I'd get home.