Most gas stations do not put any water in their gasoline because it would not make any sense for them to do so.
If the gas station added water to their gasoline to try and make the gas go further and profit further then it could cause damage to their gas pumps as well as damage to customers cars.
The damage to the gas pumps and to the customers vehicles would cost more than what little profit they would make off the gasoline they added water too.
I do know of an old guy who used to own a gas station and I caught him before adding water to the gasoline and I turned him in with video footage and he got shut down.
I used to buy gasoline as his gas station and then my truck would start running rough and turns out it was water added to the gasoline.
He's dead now of old age but most legit gas stations will not put any water in their gasoline.
It is possible however in rare cases if a gasoline tank were to leak somehow then some water might get into the gas tank or if the fuel tank lid was not secured properly then water could get into the gas tank.
or if a gasoline tanker truck was filling the gas tanks when it was raining then small amounts may be able to get into it but very unlikely there as well.