Fuel sampling
I too am a little worried about the first refuel of the day out of the fuel tanks into the aeroplane.
I place I used to fly at had a tank that was notorious for collecting water overnight.
However. If you fly at a larger airport where the fire crew are re-fuellers. They will generally check the tanks for water,density etc every day before anyone pulls up.
If this is representative i would suggest having a word with them about the checks they do as its quite interesting.
If not, i am not too sure that it takes hours or days for water to settle in a tank. I certainly, from the example above cleared water from the tank after re-fuelling, relatively quickly.
Although, i could find myself being stood correctly