Mangroves are among the most carbon-dense ecosystems on Earth, yet they thrive under a constellation of simultaneous abiotic stresses. Understanding how mangrove species regulate water use is therefore pivotal to quantifying ecosystem carbon flux, predicting responses to climate change, and guiding evidence-based restoration practice. This review synthesizes four decades of research on (i) the mechanisms and interspecific variation of water uptake, xylem transport, and stomatal regulation in mangroves; (ii) the coupling between canopy water use and carbon assimilation across spatial scales from leaf to stand; (iii) environmental drivers—particularly vapor pressure deficit, salinity, temperature, and radiation—that modulate this coupling; and (iv) the contrasting water use strategies of native versus introduced mangrove species. Key findings from the literature indicate that mangrove stomata exhibit a universal negative power-law response to vapor pressure deficit, with genus-specific sensitivity exponents ranging from −0.42 to −0.91, placing mangroves in a distinct sector of the global stomatal sensitivity spectrum. Whole-tree sap flow density varies more than tenfold across genera, and introduced species such as Sonneratia apetala and Laguncularia racemosa transpire 3–6 times more water than conservative native species at comparable stand densities, with correspondingly lower water use efficiency (1.1–2.4 versus 2.6–6.2 g C kg⁻¹ H₂O). Carbon–water coupling follows an asymptotic relationship, whereby net primary productivity saturates at high canopy conductance, generating a fundamental productivity–efficiency trade-off. Under projected climate warming and increasing vapor pressure deficit, these patterns imply differential vulnerability among mangrove genera and highlight the importance of water use strategy in shaping ecosystem carbon balance.