Not necessarily, right now it&#x27;s more economical to reform it out of natural gas or other fossil fuel so it&#x27;s not like hydrogen fuel would take water in that&#x27;s turned into hydrogen.<p>But even if efficient catalyst driven electrolysis  were used to generate hydrogen for fuel, it&#x27;s not likely that the water would be extracted from the air, they&#x27;ll suck up liquid ground water that wouldn&#x27;t necessarily have ended up evaporating into the atmosphere. So the water generated by hydrogen burning cars will end up as extra water vapor that wouldn&#x27;t have otherwise been emitted.<p>But, gasoline burning cars already emit almost a gallon of water vapor for each gallon of fuel burnt, so depending on the efficiency of the hydrogen cars, there could be a net decrease in water vapor emitted. (I&#x27;m not sure how much hydrogen a car would use to travel an equivalent distance as a gasoline powered car)