Deep Martian aquifers harboring liquid water could hold vital insights for current and past habitability. We show that with seismo-electric interface responses (IRs) we can quantitatively characterize subsurface water on Mars. Full-waveform simulations and sensitivity analyses across diverse Martian aquifer scenarios demonstrate the technique’s effectiveness. In contrast to how seismo-electric signals often appear on Earth, Mars’ desiccated surface naturally removes co-seismic fields and exposes useful IRs that allow us to characterize several aquifer properties. Changing the aquifer depth, thickness, or quantity changes the IR arrival times or shape: aquifer depth is a strong control on evanescent IRs, thickness affects the relative timing of IRs, and increasing the number of aquifers introduces more dipole sources to the waveform. Other factors, such as aquifer saturation, chemistry, and salinity, strongly affect IR amplitude but have minimal or no effect on waveform shape. Notably, for a deep low-porosity aquifer, the salinity and brine chemistry (perchlorate versus chloride) are the strongest controls on signal amplitude. Analyzing the effects of epicentral distance shows that radiating and evanescent IRs separate at large source-receiver offset, allowing analyses of both signals and accurate event distance derivation. From this numerical investigation of the sensitivity of IRs to deep Martian aquifers, we anticipate future analyses of electromagnetic data from the InSight lander or future missions to Mars and other planets.