This is a great project to do and as I see it, a good way to spend some time to tinker around and get yourself a stove which also serves as a water heater for your needs. The idea is quite simple actually and you don't even have to fashion a concrete or metal stove although the latter maybe more better as it lasts longer than concrete that might crack.
The video explains it as well as how the rocket stove works. So you just needed a coil that coils around inside the stove and it is connected to the water source or container which you wanted to be heated. It is better to insulate the container so that the heat will remain there in an extended period of time.
The water source must be higher than the stove so that we can get a natural pump as the water heats up and expelled into the water container which will then siphon cold water from container in the process.
It is a good system if you want to use firewood for heating your water and at the same time cook with the fire that is being generated by the firewood. If I was just able I would have done this myself but it is just fun to share this thing if somebody wants to spare some time with creating this kind of home essentials for heating and cooking