Have you seen ads claiming you can increase your car’s gas mileage at least 25 percent by purchasing a device and simply adding water? Apparently, folks in Wisconsin have been talking about them.
An article from a Fond du Lac news site stops just short of calling “phooey” on the claims, noting that when Popular Mechanics put a $399 “water car” device to the test, the vehicle “gave 20 fewer horsepower and about 20 percent poorer fuel economy.” Here’s the study, published in 2005. A senior editor for the same mag wrote this in a 2006 blog: "Yes, you can make hydrogen from water. But it requires a lot of electricity, expensive electricity, more expensive than burning gasoline, so what's the point?"
Consumer Reports and the EPA have tested similar devices. CR’s conclusion: The best way to get the most from a tank of gas is to follow the vehicle manufacturer's service schedule.