In case you didn't know:

Never buy gas when a tanker truck is in the station filling the tanks.
Most gas station pickup tubes are set 12" off the bottom of the tank. The water and debris settle to the bottom. Gas station operators have to check and record the debris level at least 1 time a week, its part of the annual requirements checked when the pumps are certified to deliver 1 gallon of gas for each gallon the pump shows. If the debris reaches a certain level, the tanks need to be cleaned.

When the tanker is filling up the tank, the water and debris are mixed up in the tank, and it generally takes about 1/2 hour after the fill up for it to settle back to the bottom, about the same amount of time it takes the guy to pick up the fill hoses, fill out the paper work, and leave.
If you fill up while the tanker truck is filling the tank, the odds of getting bad gas increases 10 fold. Gene