We focus on the evaluation of photosynthetic organisms. Some species and tissues can endure periods of the dry season because they rely on a robust dynamics of metabolites. The metabolic dynamics are complex and challenging to address because it involves several steps, usually with hundreds of metabolites. The metabolites densities vary among species and tissues and respond to external conditions, such as an environmental stimulus like water supply. Understanding these responses, particularly the desiccation–rehydration processes, are important both economically and evolutionarily, especially in the presence of climate change. Therefore, we propose a new way to analyze the dynamics of metabolites with a compartmental model which explores the metabolites densities’ dependence on water explicitly. We use a mathematical formulation to model the dynamics among three essential metabolites classes: sugar ([Formula: see text]), active metabolite ([Formula: see text]), and reserve accumulation ([Formula: see text]). Through stability analysis and numerical solutions, we characterize regions on the phase space, defined by the transition rates between the classes [Formula: see text] to [Formula: see text] and [Formula: see text] to [Formula: see text], where the system diverges or approaches zero. We show that different species and tissues respond distinctly to desiccation processes, being more or less resilient according to the transitions rate between the compartments of the model. Furthermore, the effects of water supply fluctuation, due to the desiccation–rehydration processes, show that unless the organism has a robust reservoir metabolism, the system cannot support itself for a long time. Many results corroborate experimental observations, and others provide a new perspective on the studies of metabolic dynamics, such as the significance of the reservoir metabolism. We understand that knowing the organism’s response to abiotic changes, particularly that of the water supply, may improve our management of the use of these organisms, for example, in the crop field during climate changes.