It is possible that adding water to a gas tank could ruin an engine, if the water is able to get past the fuel filter and into the cylinders. When the water reaches the cylinders, it will create steam, which can cause the pistons and other engine components to warp or break. If you are unsure about whether or not your car can handle water in its gas tank, it is best to play it safe and refrain from doing so.

Water can corrode the metal components of your engine, which will eventually lead to breakdown and failure. In addition, water can cause fuel gelling, which means the fuel will thicken and become solid in cold weather conditions. This will prevent your engine from starting.