Water in the gas tank may lead to the car bucking, stalling or not starting at all, or starting the car could be difficult. This is because the water and fuel separate, especially when the car has been sitting for a while, and the water sinks to the bottom with the fuel on top.
What liquid will ruin a car engine?
If you are just mischievous and does not really want to destroy the engine, use sugar or any other sweet, sticky liquid. Sugar in a gas tank is an urban legend and it will clog up the fuel filter, just like other sticky sweet liquids such as honey, molasses, waffle syrup, pancake syrup, and similar things.