This question has been in my mind for at least a year. My friend told me that water fuel engine has been developed but can't appear on the market because it will reduce the oil companies' profit and use too much water to cause water problem all over the world.

Is this true that the water fuel engine has already existed??

i think you're talking about the fuel cell engine. It runs on hydrogen gas. The by-product is water. It is not practice for a water fuel engine because the amount that is being uses is the same as the amount the water will create.

its possible but ypu would have to do a turbin that pushes the water through and yeah its point less...

ahhhhhh time to give you the lowdown. . . .
MANY amazing inventions have been invented and patented and then bought out and never seen again.
I know sum1 who worked at Ford, and he rememeber seeing some guy who had invented a car which ran on water. . . . simialr to a fuel cell. . .but Ford bought out the Patent to the technology, and it was never seen again . . why?. . . because it would harm OIL produces profits . . .
Same with lightbulbs. . . . someone invented an ever lasting lightbulb. . . . the tehcnolgoy was bought out by a bulb co0mpany and never seen again . . . why?. . because if everyone bought them, they would go out of buisness. . . .
its quite sad how such efficient inventions and ideas are all swept udner the carpet because people would loose money. . .

yeh i think so i heard about it somewhere i think in the newspaper

I've heard about multiple variations of the "water" fueled engine, including different hydrogen engines and the most popular fuel cell design. But haven't heard anywhere that it'll use so much water that its a problem! One thing to note is that you physically cannot destroy water. You can change the form and appearance and even react it to other elements but you can always get it back

that is not true. Because when you break down the molecules to release the energy. Some of the mass will convert into ENERGY (that's how you get energy). So therefore, you will have less water. BUt water is an abundant source so it's nothing to worry about and it's easy to make water anyway.

jeez, i though you were going to do a post on steam engines. take a look at
this, converting your car to tap water powered. I wonder if this even works.

A water engine is very unrealistic, it probably exsist but it would serve no purpose. The water engine would have to do vast amounts of water to propell a car and the car size would increase by like 5x to beable to support enough water to last as long as a full tank of gas. On the other hand though the fuel cell is becoming very popular and the by product of hydrogen of course is water. The main issue with these fuel cells is that its extremley dangerous, although they have done a good job of reducing the risk with a very secure cell. Although when a hydrogen station explodes its alot different from a gas station, it would cause a much greater explosion. Take for example the hydrogen bomb thats what could be caused if something were to go terribly wrong.