In any calculation of consumption, it must be taken into account that the means of transport must be returned anyway. And since this is a What if section - I don't see that it is impossible to create an (almost) closed water-steam cycle, after all, some steam cars (passenger cars) did (unlike, for example, the Sentinel wagon) have such systems. That the water in these systems needs to be replenished, but not in quantities like the Sentinel wagon, where (if I'm not mistaken,I) all the steam (water) was consumed end expelled.