It is important to emphasize that the exergy potential of the "working substance" cannot be specified per se, but only in relation to the state of the environment. A necessary condition for an existing exergy potential of the working material is, however, that it is not in thermodynamic equilibrium with the environment, i.e. there is an "entropy pressure" that stimulates the development of the system towards equilibrium.
The idea of a water engine
To be continued ...