Groundwater hydrogeochemistry of coastal aquifers (Plio-Quaternary, Turonian, and Hauterivian) of Essaouira basin, Morocco, was investigated to evaluate the groundwater quality for drinking and irrigation uses as well as to determine the key processes controlling its mineralization. The study reveals that the rock-water interaction processes (dissolution of evaporite and carbonate minerals), evaporation, reverse ion exchange mechanisms, and seawater intrusion are the main processes responsible for groundwater mineralization, reflecting from their hydrochemical facies. Water quality index (WQI), sodium percent (%Na), sodium adsorption ratio (SAR), permeability index (PI), and Kelly index (KI) ratios were applied to assess the groundwater for drinking and irrigation purposes. WQI shows that the groundwater is of poor quality and unsuitable for direct usage, necessitating prior treatment before consumption. Based on %Na, SAR, PI, and KI, the groundwater remains adequate for agricultural purposes. The stable water isotopes (18O and 2H) identified the main salinization mechanisms present within the aquifers, namely marine intrusion and evaporite dissolution. Also based on the isotopic values, the preferential recharge altitudes of the aquifers were estimated (Plio-Quaternary aquifer between 240 and 950 m a.s.l., Turonian aquifer from 590 to 890 m a.s.l., and Hauterivian aquifer between 120 and 900 m a.s.l.). Thus, it is imperative to pay great attention to the processes of groundwater salinization to fight against environmental degradation. The approach followed as well as the results of this study remain valid for better and sustainable management of the vital resource, within the Essaouira basin and similar basins.