[Christ]

An evaporated water collection system could be put in the exhaust stream to recycle most of it, but then you're getting into a very complex exhaust system, I'd think.

Of course, the heated water could be used to get some of the exhaust energy back, and any exhaust-driven applique before the water tank would help to cool the exhaust before getting to the tank, making turbochargers and the like more common, as they would help cool the exhaust so as to not boil off the water so quickly.