  (Abridged) The star-formation rate (SFR) quantitatively describes the
star-formation process in galaxies. Current ways to calibrate this rate do not
usually employ observational methods accounting for the low-mass end of stellar
populations as their signatures are too weak. Accessing the bulk of
protostellar activity within galactic star-forming regions can be achieved by
tracing signposts of ongoing star formation. One such signpost is molecular
outflows, which are bright in molecular emission. We propose to utilize the
protostellar outflow emission as a tracer of the SFR. In this work, we
introduce a novel version of the galaxy-in-a-box model, which can be used to
relate molecular emission from star formation in galaxies with the SFR. We
measured the predicted para-H2O emission at 988 GHz and corresponding SFRs for
galaxies with LFIR = $10^8$ - $10^{11}$ L$_\odot$ in a distance-independent
manner, and compared them with expectations from observations. We evaluated the
derived results by varying the star formation efficiency, the free-fall time
scaling factor, and the initial mass function. For the chosen H2O transition,
relying on the current Galactic observations and star formation properties, we
are underestimating the total galactic emission, while overestimating the SFRs,
particularly for more starburst-like configurations. The current version of the
galaxy-in-a-box model accounts for a limited number of processes and
configurations, that is, it focuses on ongoing star formation in massive young
clusters in a spiral galaxy. Therefore, the inferred results, which
underestimate the emission and overestimate the SFR, are not surprising: known
sources of emission are not included in the model. To improve the results, the
next version of the model needs to include a more detailed treatment of the
entire galactic ecosystem and other processes that would contribute to the
emission.
