Almost surely a loose or corroded connect or the sensor at the fuel filter/separator. If wetness gets in, it closes the circuit and the light comes on, even though there is no water actually in the fuel. Usually just removing and reinserting the wire harness plug to the filter will fix it, though maybe have to do it 3-4 times if its not obviously loose. Some wire grease on the fitting can't hurt either. More than likley, though, it's just a disconnected or poorly connected plug-in.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC