The water content of a cell depends on the sort of job the cells does and the intracellular apparatus it uses to do that job. Cell water is not consistent cell to cell within the same organism.
Physiol Chem Phys Med NMR. 2004;36(1):1-19.
What determines the normal water content of a living cell?
In contrast, the PM theory (Theory V) can explain readily the
specificity of water content: a specific amount of water accumulates
in a specific kind of cell because the free energy of water adsorption
on the specific proteins in that type of cells is most favorable. In
the PM theory, the quantity and kinds of proteins determine the total
amount of water in each type of living cells. Accordingly, the PM
theory anticipates that cells serving the same physiological function
have similar assortments of proteins — even among different living
organisms. On the other hand, cells serving different physiological
functions even in the same organism would have different profiles of
the kind and amount of proteins. In fact, Ling, Reid and Murphy (1986)
have already confirmed this anticipation 18 years ago. Their figures
are reproduced here as Figures. 2, 3 and 4..
Cell water is complicated and interesting but I do not think you can use it alone to explain why your organisms are one way or another.
But: you can state your organism is a certain way and then, if it is that sort of fiction, reference the cell water state as part of that cellular phenotype.