That's a good question! I know the few times i have seen a large amount of water in the sample, it did not seem to have taken on any of the blue.
Which brings up a point. i think it would be a good idea for instructors to demonstrate this by putting some water in with the fuel in the sample cup so you can really see what it looks like. All during my training, it never came up so I just kinda assumed I'd know what it looked like. It happened for real once, and it stood out very plainly. It looks like this:
So i would say probably not Ada, even if the tanks were half full of water, the result would be the same, ie the water would not mix with the fuel and pick up the dye. There is also the smell, which would be much fainter.
As you are somewhat of a scientist about things, give yourself a few more data points and try it out. It's pretty cool to see, and i know i feel much more comfortable now that I know what it looks like for sure!