I believe it is the Department of Agriculture that monitors the fuel stations and their pumps. I do not know how much this varies state to state, but here they have some pretty strict requirements. A family member had an Amoco franchise and took the buyout from BP when the opportunity arose, and they are even more strict than the law requires.
The ground tanks have all kinds of sensors, not only for water but for flow rates for both the delivery pumps (prime pumps) in the ground as well as the actual pumps in the islands. Substandard fuel would tear them up just as bad, so they make very sure that does not happen.
Now if you are filling your modern Volkswagen with some above ground farm tank from the 1960s that your old uncle used to use to fill up his old John Deere, then yes you may open yourself up to a problem. But otherwise, the modern high volume fuel retailer of a reputable name brand is not likely to ever become even a "marginal" problem within any normal lifespan of any car or light truck. If it was, my lot would be jammed packed with broken down diesels with fuel related problems. And that does not happen.
Now what HAS happened, many times, is some dumbassed aftermarket fuel filter conglomeration that someone slapped on their TDI with science experiment pieces and tractor parts has caused a loss of fuel prime, no starts, hard starts, leaks, etc. Those of course get tossed in the trash and the car runs perfectly fine after the factory setup is put back in place.