more like a condensation or rain/ground water seep in to the tank

or no maintenance done to the tank

water is usually at the bottom below the fuel intake

no one purposely add water

hence they need to do the maintenance to suck out the water from the tank. if they know water gets in they need to do more maintenance.

once water level goes, up water gets in the the cars, cars will die as pistons cannot compress water.

it is not a tactic to cheat as you cannot balance the water/fuel mixture
this put water in petrol are old man tales from olden time where people who have no education