What @
Tcoat said....
In addition, if you are really concerned, it's easy enough to test. Fuel has smaller molecules than water or debris so there are lots of ways to strain test it. This is common in small plane aviation. Fuel tanks are tested before every flight for water using a strainer similar to this
GATS Jar.
Nearly all fuel has some level of water in it. Just condensation in the storage tank or your fuel tank will add water. That is why it is normal practice to always fill the tank of a small plane before you park it overnight.
Parked for a few hours with half a tank, condensation will form, and water being heavier, will separate into the bottom of the tanks. What happens in a small plane is that you'll have enough good fuel to run for start-up and take-off, then you will hit water in the lines at just the "perfect" time for a very short flight.
If the pump did have a "water detection system" it would most likely be a "water straining system" because it would not be that difficult to engineer following the same process as the fuel tester I mentioned above, or a fuel strainer which also filters out water and other solid contaminants.
As @
Tcoat mentioned the real risk comes from using low turn-over stations. They are the ones most likely to have half full tanks underground where condensation has a chance to introduce water. That's a real risk in aviation if you fly "back country" or to a rural airport with only a handful of flights and fuel purchases a week.