Freshwater scarcity remains a critical challenge in coastal regions, particularly in developing nations. This study investigates kaolin clay, a locally available and cost-effective material, as a sustainable adsorbent for coastal water desalination. Raw and activated kaolin clay was characterized using X-ray diffraction (XRD) and SEM. Fresh coastal water was collected and characterized for physicochemical parameters, including salinity, pH, turbidity, total dissolved solids (TDS), and major ionic species. Batch adsorption experiments were conducted to evaluate the effects of contact time, adsorbent dosage, temperature, and feed water concentration on salt removal efficiency. The adsorption data were analyzed using the Langmuir and the Freundlich isotherm models. Results showed that activated kaolin achieved 65% salinity removal within 30 min of contact time, with maximum removal efficiencies of 76.8% at 3 g/100 mL adsorbent dosage and 78.1% at 60 °C. The adsorption process followed the Langmuir and the Freundlich isotherm models with high correlation coefficients (R2 = 0.9961). The results revealed that the Langmuir isotherm provided a better fit to the experimental data with correlation coefficients (R > 0.85) for activated kaolin clay. These findings demonstrate that kaolin clay is an effective, energy-efficient, and economically viable adsorbent for treating highly saline coastal waters, offering promise for resource-limited communities requiring affordable desalination solutions.