A water-fuelled car is a hypothetical automobile that derives its energy directly from water. Water-fuelled cars have been the subject of numerous international patents, newspaper and popular science magazine articles, local television news coverage, and the Internet. The claims for these devices have been found to be incorrect and some were found to be tied to investment frauds. These vehicles may be claimed to produce fuel from water on board with no other energy input, or may be a hybrid of sorts claiming to get energy from both water and a conventional source (such as gasoline).
This article focuses on vehicles that claim to extract chemical potential energy directly from water. Water is fully oxidized hydrogen. Hydrogen itself is a high-energy, flammable substance, but its useful energy is released when water is formed—water will not burn. The process of electrolysis, discussed below, would split water into hydrogen and oxygen, but it takes as much energy to take apart a water molecule as was released when the hydrogen was oxidized to form water. In fact, some energy would be lost in converting water to hydrogen and then burning the hydrogen because some heat would always be produced in the conversions. Releasing chemical energy from water would therefore violate the first and/or second laws of thermodynamics.
