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The aim of this present study was to evaluate groundwater quality in the upstream part of the Essaouira basin. A detailed geochemical study of groundwater region is described, and the origin of the chemical composition of groundwater has been qualitatively evaluated, using multivariate statistical methods (PCA, HCA), and Water Quality Index (WQI) was used to determine the suitability of water for drinking. To attempt this investigation, 38 samples were analysed for various physicochemical parameters such as temperature, pH, TDS, Na, NO 3 , K, Ca, HCO 3 , Cl, Mg, and SO 4. The results obtained showed that the facies characterizing the study area was a combination of Ca-SO 4 and mixed Ca-Mg-Cl. Hydrochemical approach based on the bivariate diagrams of major ions indicates that the origins of groundwater mineralization are the result of (I) evaporite dissolution; (II) cation-exchange reactions; and (III) evaporation processes. The WQI values range from 82.3 to 390.9, and therefore the water samples can be categorized into five groups: excellent water to water unsuitable for drinking. In global, 61% of the groundwater sampled had poor water quality, 18% were very poor water quality, 16% are unsuitable for drinking, and just 6% represent a good quality. However, the results of this paper indicate that most water is not safe for drinking and needs further treatment.

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In this study, hydrogeochemical analyses were combined with geographic information system (GIS) tools to investigate salinization sources of groundwater in the downstream part of the Essaouira basin, and to analyze the spatiotemporal trends in groundwater quality. To assess groundwater suitability for drinking purposes, the quality of sampled water was compared with the World Health Organization (WHO) and the Moroccan guidelines. Wilcox and US salinity laboratory (USSL) diagrams were used to evaluate groundwater suitability for irrigation. Hydrogeochemical analyses revealed that groundwater is of Na-Cl and Ca-Mg-Cl types. The analyses of the correlation between the chemical elements showed that the water–rock interaction and the reverse ion exchange are the major processes impacting groundwater degradation in the study area. The study of groundwater suitability for drinking and irrigation purposes shows that groundwater quality in the study area is permissible, but not desirable for human consumption. Additionally, groundwater is permissible for agricultural use but with high-salinity hazards. The spatial distribution of the physicochemical elements shows a general upward gradient from the north to the south and from the east to the west. The trend in groundwater quality during the last five years shows a shifting in the quality from the mixed Ca-Mg-Cl to the Na-Cl type.

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