No, your car can't use water as fuel
No matter how you try, you can't beat the laws of the universe!
You will find people peddling a system that uses some of the electricity generated by the vehicle's alternator to electrolyse water - i.e. split it into its component elements, hydrogen and oxygen. The hydrogen is then injected into the air intake to supplement the engine's normal fuel.
The people who push this system will tell you that you are getting free fuel from the water. You aren't. Some of the engine's power is used to drive the alternator. Now the alternator, in common with machinery, is not 100% efficient. That is to say, it does not convert all of the energy it gets from its drive belt into electricity: some is lost as heat due to, for example, friction in the bearings and electrical resistance in the copper windings. That energy was provided by the motor burning fuel - so a small amount of fuel was wasted during the process of generating the electricity. Not all the electricity used to electrolyse the water actually does useful work - some of that is simply dissipated as heat due to the imperfections of the process and the resistance of the water itself. So a bit more fuel is wasted.
A molecule (the smallest unit of a compound) of water consists of two atoms of hydrogen and one of water, thus the famous formula H2O. In combination like this, the atoms are in a lower energy state (i.e. they move more slowly) than they would be if free. The process of electrolysis breaks the water into its constituents of hydrogen and oxygen by giving the atoms more energy so they can break the bonds that hold them together. The power in the electrical current is used to do this - so the gases become a kind of battery, storing energy.
It's obvious that just venting the oxygen to the atmosphere simply "throws away" that energy. The energy stored in the hydrogen is recovered by burning it as fuel but - and this is the killer - you can't get more energy out of it than you put in during the electrolysis process.
So what you've got is: you're using a little more gas to generate a little more electricity than the engine/alternator otherwise would. A large part of that energy gets diss[pated (wasted) as heat. A fraction of it is recovered by burning hydrogen in the engine. You'd have been better off using the wasted gas to drive the car in the first place!
These systems do not give you better fuel consumption/gas mileage: they make it worse. There is no way to circumvent the simple laws of physics that make this so, no matter what some people might say.
You can get better results by following some simple rules (there are others but that's not really what this hub is about):
- accelerate and brake gently
- make sure your tyre pressures are correct for the load you're carrying and the typical speeds you do
- make sure the engine is serviced correctly when it needs it, especially for things like air and oil filters
- don't carry around stuff you don't need in the vehicle - you're paying to accelerate it every time you put your foot down and you're wearing your brakes out a bit more each time you slow down.
- change to a lighter vehicle with a smaller, more efficient engine!