Water is very slightly "soluble" in gasoline, so there's the possiblility of some water intimately contained in the gas. Alcohol added to the gas can increase the amount of water, and may result from using a "gasohol" or from adding something like Dri-gas. In either case, the alcohol can evaporate, esspecially in a tank that's only part filled, resulting in water original held in solution in the alcohol/gas mix that's "no longer soluble."

When "stirred," as when the tank is filled, the water can be broken into small droplets intermixed with the gasoline, "in suspension" much as a colloidal powder can be held in a liquid. Water percentage in this case can be quite high, and 40% isn't really too surprising.

The "suspended water" will eventually coalesce into larger droplets, big enough to settle out so that the water is (nearly) all at the bottom and the gasoline floats on top. In a large tank, however, this "settling" can take several hours. If your tankful is extracted before the settling/separation occurs, you can get a mixture with a rather high water content.

Left to settle in the vehicle, the mixture should again separate, and some water in the bottom of a vehicle tank is an expected condition.

If you've run your vehicle "down to the water," introducing even dry fuel may produce enough mixing that for a time after the fill, the fuel getting to the engine may have a high moisture content¹. With enough water in the vehicle tank, the fuel system may begin to pick up nearly "all water" pretty much continuously.

The highest cost repair procedure, commonly recommended by service shops, is removal and steam cleaning of the fuel tank. In my experience, this is seldom truly necessary; but as noted I have little experience with some of the latest innovations in tank/fuel system designs.

Fuel filters almost always should be replaced, and if there's injector damage their replacement can be expensive. Getting as much of the water as possible out of the tank, which may require disconnecting lines for adequate draining and "siphon-sponging" some residual, has been adequate for older vehicles I've seen.

For a shop that's well equipped to do it, the steam cleaning may result in lower labor charges than a piece-by-piece fix, so local advice appropriate to your situation is the only thing that works.

¹ Service shops sometimes see an increase in "watered gas" calls when there's been a jump in fuel price. People put of filling up until they're down to nothing but the normal tank bilge, which is mixed and suspended when they do add fuel, giving the impression that the station gas was the source of a lot of water.

John