I'm an engineer too, and saw "dirty" gasoline, phase separation, and pumping out tanks of water contaminated fuel. You get some funny reactions between water and fuel additives, too.
The pickup in a fuel storage tank at a gas station is above the bottom floor of the tank, so that if there is water, it is supposed to sink below the pickup and customers only receive gasoline. Periodically the station is supposed to pump out the water bottoms. If something happens to where the fuel becomes saturated, the 3% water bottom suddenly becomes 6% water+alcohol and the station pumps that mix into cars.... arrgh.
That probably doesn't happen anymore, since the use of alcohol blends has "dried up" all the tanks, but when gasohol first started, it was a distribution system problem.