If it sounds too good to be true, that’s often because it is. You may have recently heard about a new car fueled entirely with water. Early reviews of the vehicle created by the Japanese company Genepax promoted it as one that would continue cruising as long as there was bottled water in the vehicle to pour into the energy generator in its tank.

But, this so-called breakthrough was quickly exposed for what it really is: A gimmick that, in practice, would require so much money and energy to work that it has no place in the world of everyday people looking for practical and affordable ways to reduce fuel consumption.

This reviewer was quick to note that, in order to run on water, the car must carry a heavy and expensive electrolyzer on board and that it would ultimately require an outside source of energy – a lot of it – to “break” the water down into a usable fuel. In other words, the fuel used to render the water usable would most likely exceed the amount of fuel needed to power a conventional gasoline-powered car. So much for that.

This does not mean that it is impossible to build a better, more fuel efficient car using advanced technologies. Indeed, technology will be the key to fueling our future. But it does suggest that even as we do discover creative ways to do more with less, there will be tradeoffs. As we have seen with electric cars, higher costs and limited range are tradeoffs that the typical consumer often cannot afford to make. Not to mention that it takes energy to make electricity. Yes, technology will continue to improve, sometimes at a breathtaking pace. However, for the foreseeable future, there does not appear to be a magic bullet that will render transportation fuel-free.

The lesson behind the hype of the Genepax vehicle that runs on water is one that goes beyond just automobile transportation. When considering energy efficiency, we must consider the big picture: Not just the amount of energy we consume, but other factors, like the massive amounts of energy required to turn water into fuel, or the amount of oil it takes to transport imported foreign oil to our shores. Likewise, when considering promising new technologies, we must consider whether they could be produced and adopted on a large scale.