If you get water with your gas from a station, the station has a real problem. They should be testing it regularly in this area because of high humidity. When the tank is left slack, a lot of air space, for long periods the air above the fuel condenses and water accumulates at the bottom. This is bad but shouldn't be a problem because the suction line is above the tank bottom far enough not to pull water unless water is allowed to accumulate instead of being stripped before it gets deep enough to be sucked up into the line that feeds the pumps.
Another source of water getting into the tank is by a leak due to tank deterioration, rust through the shell on steel tanks or a break in the fiberglass of a fiberglass tank. These leaks have to be recognized and action taken to eliminate them and counter the accumulation of water in the bottom. A third source is through the fill fitting at the ground level, unlikely unless water is allowed to accumulate on the concrete around the fill opening. Even more unlikely is the fuel supplier delivering water with the fuel. Testing fuel, tank maintenance and operational excellence are critical.