BAD IDEA
Can I fill my car with water?
Nope. Filling your car with water is a brilliant way to ruin your engine fast.
Your car's engine runs on gasoline or diesel, not water. Putting water in the fuel tank won't make it quirky or eco-friendly; it'll just clog things up and leave you stranded. Engines and water mix about as well as oil and, well, water. So, don’t try to save a few bucks by watering down your gas tank — it's just sabotage.