Introduction

Groundwater resources constitute significant water reserves, both quantitatively and qualitatively (Hamed et al. 2013; Bouaicha et al. 2019). Groundwater provides almost 50% of all drinking water worldwide and 43% of all consumptive agricultural use of water (Smith et al. 2016). Preserving the quality of groundwater is therefore a major concern for public health reasons (Bahir et al. 2018a; Carreira et al. 2018). Coastal aquifers serve as major sources for freshwater supply in many countries around the world, especially in North Africa has been marked by continuous decreases of water levels in coastal aquifers reaching alarming values (Bahir et al. 2020; El Mountassir et al. 2021b). Many researches have been conducted to reveal the hydrochemical characteristics, water quality, chemistry components controlling mechanisms (Bahir et al. 2019; El Mountassir et al. 2021c; Ouarani et al. 2020).

At our national level, Morocco is mostly under arid and semi-arid climate, thus experiencing water stress (Agoumi and Naji 1998) due to prolonged periods of drought. Moreover, Morocco is ranked 139th out of 179 countries under water stress (FAO 2014). The isotopic technique shows that groundwater recharge in the study region is provided by ocean precipitation without substantial evaporation and that the impacts of climate change have not preserved the isotopic signature (Bahir et al. 2019, 2021a; El Mountassir et al. 2021a, c).

Water quality degradation poses major health and environmental issues (Yang et al. 1999). Nitrate pollution in groundwater has been a major environmental problem worldwide (Panno et al. 2001; Zhang et al. 2015; Sakram et al. 2019; Bahir et al. 2018b; El Mountassir et al. 2021b). It is generally believed that groundwater generally has a higher quality. However, there will be a certain connection channel between the surface and groundwater. Owing to the use of fertilizers, nitrate has been related to agricultural activities. However there are other urban development-related sources that may increase groundwater nitrate concentrations. Research has shown in recent years that nitrate concentrations are equivalent or even higher in some urban aquifers than in the rural areas surrounding them (Ford and Tellam 1994; Lerner et al. 1999). On-site sewage treatment, leaky mains, leaky sewers, polluted land (landfill waste disposal), industry, river or channel aquifer interaction, house construction, and the use of urban fertilizers are non-agricultural sources of nitrate in groundwater (Mazari and Mackay 1993; Barrett et al. 1999; Yang et al. 1999; Wakida and Lerner 2005).

The study area is dominated by karst aquifers and is particularly vulnerable to contamination by nitrates of anthropogenic origin due to the rapid movement of water in their network of conduits (Bahir et al. 2019). Karst aquifers are very sensitive to pollution and human effects (Kačaroğlu 1999; Ford and Williams 2007; Williams 2009; Chapman et al. 2015). Given that karst aquifers provide 25% of the world's drinking water (Van Beynen 2011), it is extremely important to characterize and understand the pollution processes in karst groundwater. A big problem in Morocco is the depletion of groundwater aquifers. The rapid decrease in groundwater levels on average 0.5–2 m per year is usually due to: (a) low groundwater recharge and (b) over-expansion of Morocco's agricultural activities (Ait Kadi and Ziyad 2018). Several researchers who have worked on the Essaouira basin, they have found that there is a clear drop in the level of the water table with also a deterioration of its quality, in particular pollution by nitrates in the part where farmers still use flood irrigation. Nitrate was less than 50 mg/L in some part which can be explained by the adoption of the drip irrigation system. The main objectives of the present paper are:

  1. 1.

    to study the spatial distribution of the nitrate and salinity in Meskala-Krimat sub-basin.

  2. 2.

    to study the influence of rainfall pattern in the piezometric surface, salinity, and nitrate fluctuation.

  3. 3.

    to assess the risk of the Essaouira groundwater bodies to human health and their suitability for drinking purposes by the use of guidelines for drinking water quality of World Health Organization.

The objective is to raise public and institutional awareness in terms of the effectiveness of nitrogen management policies. The information could be beneficial for groundwater management worldwide.

Materials and methods

Study area

The Meskala-Krimat sub-basin is located on the southwest of Morocco, near of the city of Essaouira (Fig. 1). The study area is considered to have a semi-arid climate with a mean annual air temperature of 20 °C, and with an average annual precipitation of 326 mm most of which occur from October to April. This sub-basin occupies an area of 1196 km2. Agriculture and tourism are the basic economic pivots of the population. Olives, argan and field crops are among the most important crops in the basin.

Fig. 1
figure 1

Location of study area

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With regard to the hydrogeological aspect, the Meskala-Krimat sub-basin is a more or less independent set of hydrogeological systems corresponding to different aquifer systems; the Plio-quaternary aquifer (shallow) is formed by the Senonian grey marls in the downstream part of the study area. And in the upstream study area, the Cenomanian–Turonian aquifer (deep) consists mainly of limestone and dolomitic-limestone layers (El Mountassir et al. 2021a).

The total area of Essaouira basin is 6355 km2 inhabited by population number of 450 527. The groundwater resource is of vital importance within the study area, since groundwater supplies irrigation and drinking water requirements. The main aquifer recharge sources are precipitation and subsurface flow from surrounding highlands and rivers among others (El Mountassir et al. 2021a). Irrigation water in addition infiltrates back to the groundwater system.

Groundwater sampling and chemical analyses

To achieve the study objectives, 196 groundwater samples from existing wells in the Meskala-krimat sub-basin were collected during 4 field trips in 2007, 2017, 2018 and 2019. The physicochemical parameters (temperature, pH, electrical conductivity) were measured using the multiparameter HI 9828 in the study area. The groundwater level was determined using a 200 m piezometric sound probe. Overall, the analytical procedures, quality assurance, quality control and precision adopted in this study were based on the methods described by APHA (1995). Before sampling, each shallow well was continuously pumped for at least 10 to 15 min to ensure that the samples were representative of the groundwater. Half liter (500 ml) of groundwater was collected from each site in polyethylene bottles that were thoroughly prewashed with deionized water. Simple refrigeration (in an icebox below 4 °C) and preservation in darkness is applied to protect the samples during their transport to the laboratory.

For the groundwater collected in 2007 (Table 1), the analyses of major chemical elements (SO4, Na, HCO3, K, Ca, NO3, Cl, and Mg) was conducted were carried out using ion chromatography at the Center for Analysis and Characterization of the Semlalia Faculty of Science in Marrakech (Bahir et al. 2007).

Table 1 Physicochemical parameters of the analyzed samples from the Meskala-Krimat sub-basin collected in 2007, 2017, 2018 and 2019   
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The data (2017, 2018, 2019) presented in Table 1 were carried out at the Ecole Normale Superieure (Cadi Ayad University, Morocco) at the Laboratory of Geosciences and Environment. Cl, CO3 and HCO3 concentrations have been determined with Mohr titration using 0.1 N HCL.

Based on the ionic balance, the results of the study were validated. The number of cation concentrations in meq/L is equal to the sum of anion concentrations within a reasonable range of errors, preferably ± 5% but acceptable up to ± 10% (Domenico and Schwartz 1990). The follow formula was used to determine the ionic balance error.

$$\mathrm{IB}=100\times \frac{\sum \mathrm{ Cations }-\sum \mathrm{ Anions}}{\sum \mathrm{ Cations }+\sum \mathrm{ Anions}}.$$
(1)

The computed ionic balance error (IB) was observed to be within the acceptable limit of ± 10%.

The maps were produced by the inverse distance weighting (IDW) interpolation method using ArcGIS version 10.2.2 software (ESRI 2011).

Results and discussion

Hydrochemical facies

In areas of water scarcity, such as semi-arid and arid environments, the problem of groundwater salinization is a global phenomenon (Hamed et al. 2018). Hydrochemical facies are a helpful method for assessing the chemistry of groundwater. It is used to describe in the chemistry of groundwater samples the similarity and dissimilarity of the anions and dominant cations of all samples (Hamed et al. 2018; Bouaicha et al. 2019). Furthermore these trilinear diagrams used for the tracing of hydrochemical data have been independently developed by (Piper et al. 1944). The projection of the analyzed samples on the Piper diagram (Fig. 2) reveals that the Ca–Cl, Ca–Mg–Cl, Na–Cl, and Ca–HCO3 facies are the majority of the samples for all campaigns.

Fig. 2
figure 2

Diagram piper of the campaigns: 2007 (A), 2017 (B), 2018 (C) and 2019 (D)

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Quality and evolution of groundwater

The quality of groundwater in the study area on the year 2019 was studied with the aim to evaluate the suitability of this groundwater for domestic use. The hydrochemical properties of groundwater sampled from the Meskala-Krimat sub-basin are shown in Table 2.

Table 2 Physico-chemical parameters of groundwater samples collected in 2019
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Water table depth ranges from 4.8 m at the point E139 in the eastern part of the study area, to 50.3 m at the point E192 in the downstream part of Mekala-Krimat sub-basin (Fig. 3). The groundwater levels decreased on average by 351% as compared to the levels of the same point E175 (7 m) measured in 2007. This decrease in groundwater level might be caused by the excessive use of shallow groundwater resources for agricultural irrigation and continuous drought in the recent years, as indicated by Bahir et al. (2020).

Fig. 3
figure 3

Variation water-table level in the study area of all samples of campaign 2019

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The pH of groundwater sampled from the study area is slightly acidic to marginally alkaline and ranged from 7 to 8.40. Table 2 shows that all samples have pH within WHO range. The pH of groundwater depends on the composition of the rocks and sediments that surround their travel pathway of the recharge water infiltrating to the groundwater (Kumari and Rai 2020). It also depends upon on how long the existing groundwater is in contact with a particular rock. The longer the contact time, the larger will be the effect of the rock chemistry on the composition and pH of the groundwater (Kumari and Rai 2020). The temperatures of groundwater sampled were generally close to ambient temperature, ranging from 14.85 to 24 °C with a mean value of 20.45 °C (Table 2).

Electrical conductivity is the most important parameter to demarcate salinity hazard and suitability of water for irrigation purpose. Figure 4 shows that most of the groundwater samples that exceeded the WHO drinking water criteria (50 mg/L) for nitrate, and similarly for electrical conductivity (> 800 µS/cm). In general, the measured groundwater electrical conductivity (EC) values showed some degree of variation, ranging from 615 µS/cm to 5738 µS/cm. So, the waters are classified as “Frech water” to “Medium brackish water”, according to the WHO standards (2011). Table 2 shows that 5% of samples have frech water are suitability for drinking (EC < 800 µS/cm) (WHO 2011), and 8% of samples have slightly brackish are suitability for irrigation water (800 < EC < 1700 µS/cm) (WHO 2011). However, the majority of sample 87% have medium brackich water (1700 < EC < 8000 µS/cm) (WHO 2011). The result of EC indicates that 7% of samples have conductivity with in WHO desirable limit, whereas 93% samples exceed the WHO maximum permissible limits (Table 2, Fig. 5d). The reason for high salinity in groundwater of these areas is be due to natural concentration of salts as evapo-transpiration exceeds precipitation in semi-arid climatic conditions prevailing in the area and the lack of drainage.

Fig. 4
figure 4

Variation in nitrate concentration and EC in the study area of all samples of campaign 2019

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Fig. 5
figure 5

Spatio-temporal distribution of EC in the study area: campaign of 2007 (A), 2017 (B), 2018 (C), and 2019 (D)

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The sulphate occurs in groundwater generally as soluble salts of magnesium, sodium and calcium. According to Adams et al. (2001), rock and soil formations may naturally contain sulphates. As water moves through these, sulphates are picked up and dissolve in the groundwater, during infiltration of rainfall and groundwater recharge (Adams et al. 2001). The sulphate in the groundwater of the study area ranges from 12.65 to 1942.06 mg/L, with an average 333.68 mg/L (Table 2) and 41.3% of the samples are above the standard values of 250 mg/L (WHO 2011). The study area have 56.89% samples of sulphate within WHO desirable limit for drinking waters and 19% were found to be beyond the maximum permissible limits of WHO standards (Table 2).

The presence of carbonates, bicarbonates and hydroxides are the main cause of alkalinity in natural waters. Bicarbonates constitute the major form because they are formed in considerable amount from the action of carbonates upon the basic materials in the soil. The bicarbonates in the groundwater of the study area ranges from 244 at the point E144 in Zerrar dam to 898 mg/L at the point E180 in Tlet Hanchane with the mean of 496.12 (Table 2). In the region, 35.93% of the samples have bicarbonate within WHO desirable limit (Table 2) for drinking waters and 64.06% were found to be beyond the maximum permissible limits of WHO standards. The high alkalinity values at few locations were due to the action of carbonates upon the basic materials in the soil.

Chloride is a significant parameter to analyze the water quality. Higher concentration of chloride denotes higher degree of organic pollution (Yogendra and Puttaiah 2008). It can be because of natural processes; the passage of water through natural salt formations in the earth or it may be due to pollution from domestic use. The chloride in the groundwater ranges from 113 mg/L at the point E175 in Kechoula region to 1817.6 mg/L at the point E161 in Meskala region with the mean of 584 mg/L (Table 2). The study area has 12.06% samples of chloride within WHO desirable limit for drinking waters and the rest 36.20% were found to be beyond the maximum permissible limits of WHO standards (Table 2).

Calcium is one of the most abundant substances in the water. Dissolve calcium and magnesium in water are the two most common minerals that make water hard. The calcium in the groundwater ranges from 43.29 at the point E142 in Meskala region to 769.54 mg/L at the point E171 in the upstream of study area (Table 2). About 98.27% of the areas have calcium above WHO desirable limit for drinking waters and merely 34.48% were found to be beyond the maximum permissible limits of WHO standards.

Sodium and potassium are essential for human health. Excess of sodium causes hypertension, congenial diseases, kidney disorder and nerve disorder in human body (Pohl et al. 2013). The sodium in the groundwater of the study area, ranges from 12.4 at the point E156 in the Meskala region to 671.1 mg/L at the point E142 in Meskala region, with the mean of 175.4 mg/L (Table 2). Only 27.58% samples of the study area were found to be beyond the maximum permissible limits of WHO standards. The high sodium values in the study area may be attributed to base-exchange phenomena (Bahir et al. 2020). The potassium in the groundwater of the study area, ranges from 0.80 mg/L at the point E175 in Kechoula region to 169.41 mg/L at the point E184 in the downstream part of the study area, with the mean of 13.83 mg/L (Table 2). In the region, 72.41% of the samples have bicarbonate within WHO desirable limit (Table 2) for drinking waters and 5.17% were found to be beyond the maximum permissible limits of WHO standards. The concentration of potassium at a few places is unusually very high in Meskala-krimat sub basin, which may be due to salt patches present geogenically and fertilizer leaching or percolating through the sub-surface.

More magnesium present in the water affects the soil quality, converting it to alkaline and that ultimately leads to low crop yields (Obiefuna and Sheriff 2011). The magnesium in the groundwater ranges from 31.66 at the point E175 in Kechoula region to 297.43 mg/L at the point E188 in Tlet Hanchane region, with mean of 116.99 mg/L (Table 2). In the study area about 17.24% of magnesium samples are within WHO desirable limit for drinking waters and just 8.62% were found to be beyond the maximum permissible limits of WHO standards.

The nitrate in the groundwater of the area ranges from 2 to 175 mg/L at the study area in Essaouira basin (Table 2, Fig. 7D). About 13.79% samples have nitrate within WHO desirable limit for drinking waters and 20.68% were found to be beyond the maximum permissible limits of WHO standards. Sources of nitrate in water include human activity such as application of fertilizer in farming practices, human and animal waste (which relate to population).

The physio-chemical characteristics of the groundwater quality play a significant role in the health of the people; therefore it is necessary to examine groundwater quality correctly. Most of the villages of the study area were unfit for the consumption of water because of high concentration of nitrate.

The spatio-temporal distribution maps of the electrical conductivity

The concentration of dissolved ions is the fundamental determinant of electrical conductivity. It is related with the aquifer matrix, the speed and direction of groundwater flow and the residence time (Bahir et al. 2020). The spatial–temporal distribution of electrical conductivity was studied to assess the impact of climate change on the groundwater quality of the study area.

The EC values for the 2007 campaign ranged from 966 to 3100 μS/cm, with a mean of 1935 μS/cm. The EC values ranged between 635 and 6776 μS/cm in 2017, with a mean of 2285 μS/cm. As for the 2018 campaign, with an average of 2448 μS/cm, EC values range between 601 and 5845 μS/cm. They range from 615 to 5738 μS/cm for the 2019 campaign, with a mean of 2454 μS/cm (Table 1).

From the analysis of the maps in Fig. 5, it can be seen that the electrical conductivity values become more and more important by advancing in time and going from east to west, and this during the four campaigns. Taking, for example, the region of bouabout, recharge area of the Cenomanian–Turonian aquifer (El Mountassir et al. 2021a), the electrical conductivity values fluctuate from 1300 μS/cm in 2007 to reach 2173 μS/cm in 2019 of the point E8 and E167, respectively. However, the general spatial–temporal evolution of electrical conductivity shows an increasing trend.

The EC spatiotemporal distribution maps (Fig. 5A–D) show that the EC values from 2007 to 2019 and towards the Atlantic Ocean are very improved. Furthermore, the study area is marked by a lack of industrial activity and agricultural activity of the “food crop” type, and it is located in the semi-arid zone, with a decrease in precipitation and an increase in temperature, causing drought and a decline in the piezometric level, the degradation of groundwater quality is primarily caused by climate change (Bahir et al. 2020).

Piezometric map evolution

The groundwater flow status is shown in the water-table level map of the study area (Fig. 6). The status of the aquifer's hydraulic gradient at different points of the plain can be assessed by consulting the water table map. One of the main parameters in the transmission and movement of soluble materials is the gradient of the groundwater flow, since a high hydraulic gradient flow contributes to a faster movement of the contaminants and hence an expansion of the pollution plume in the downstream direction (Chitsazan et al. 2017).

Fig. 6
figure 6

Piezometric maps of the study area: campaigns of 2007 (A), 2017 (B), 2018 (C) and 2019 (D)

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From the piezometric maps of the field of study, generated with campaign data (2007, 2017, 2018, and 2019), the overall direction of flow for the northern part was from SE to NW and for the southern part was from NE to SW is shown (Fig. 6). This implies that flow is conditioned by the Cenomanian–Turonian aquifer substratum and morphology. Groundwater has the same flow path with a decrease in the piezometric level for the 12-year observation period. This condition however is comfortably materialized, for example, by moving the iso-piezometric contours more and more upstream of 450 and 600 m.a.s.l, and this is observed on the four piezometric maps (Fig. 6A–D). The level of groundwater in the Essaouira basin has significantly lowered for 12 years. This change is mainly due to the decrease in rainfall (Bahir et al. 2020, 2021b).

Changes in nitrate concentrations of groundwater over a recent 12-year period

Investigating the spatial changes on nitrate contamination in the Meskala-Krimat sub-basin study area, for all the campaigns (2007, 2017, 2018 and 2019), the NO3 concentration for all samples ranged from 2 to 214 mg/L (Fig. 7). In 2007 campaign, 52% of the samples had NO3 concentration over 45 mg/L (limit accepted by WHO 2011). In 2017 campaign, 27% of the samples had NO3 concentration over 45 mg/L. In 2018 campaign, 21% of the samples had NO3 concentration over 45 mg/L. In 2019 campaign, 17% of the samples had NO3 concentration over 45 mg/L. Furthermore, Fig. 7 showed that the highest concentrations had been observed in downstream and the upstream of study area where the highest concentrations had been observed at points E2, E4, E5, E9-E12, E14, and E15 in the 2007 campaign. For the campaign 2017, the highest concentrations had been observed at points E18, E20, E23, E24, E27, E36, E40, E42, E50, E52, E54,E55, E58,E59,E61, and E67. For the campaign 2018, the highest concentrations had been observed at points E77, E82, E86, E88, E89, E97, E103, E113, E122, E124, E129, E134, and E136. For the campaign 2019, the highest concentrations had been observed at points E141, E143, E149, E151, E153, E160, E176, E184, E185, and E189.

Fig. 7
figure 7

Spatio-temporal distribution of NO3 in the study area: campaign of 2007 (A), 2017 (B), 2018 (C), and 2019 (D)

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These highest concentrations could be explained by: (1) the high concentration of fertilizers use; (2) the gap of a sewage system and wastewater treatment plant (village of Krimat and Tlet Hanchane); (3) the tourist effect; (4) the absence of a sanitation network allowing the evacuation of wastewater; (5) poor protection of wells and especially against the permanent puddles surrounding the structures which are heavily loaded with excrement from animals coming for watering and also for the water supply of the inhabitants.

Groundwater characteristics and ethics

Groundwater is the continent's most important freshwater resource and reserve. The delayed and damped reaction to external action, as well as the huge storage with a slow recovery rate, describe its quantity and quality. This is not well understood and difficult to experience personally because groundwater cannot be seen immediately (Custodio 2021). Groundwater supplies, in particular, have become vulnerable to deterioration and depletion, despite the fact that more than 1.2 billion people still lack access to safe drinking water (Abrunhosa et al. 2021). In many places around the world, the increased use of groundwater and the levels of water contamination that accompany it have exceeded sustainable limits. Today, 70% of the world's groundwater withdrawals are used for irrigation, with irrigation accounting for 40% of global food production (Abrunhosa et al. 2021).

Groundwater related issues: case study of Morocco

With the demographic and economic growth, the country’s water needs continue to increase. Desalination of seawater is an option adopted by the government to deal with the depletion of water resources. Overall, Morocco will have 8 desalination stations, which will produce 1 billion m3 of water in a few years and limit water stress. The techniques used often consume a lot of energy, most often supplied by fossil fuels, which have the disadvantage for the environment of emitting atmospheric pollutants, in particular carbon dioxide (CO2), oxides of sulfur and nitrogen, and solid particles. For this, Morocco using intermittent energy such as solar or wind power requires a large storage capacity by batteries to ensure permanent power. According to UNESCO report 2019, seawater desalination is a growing danger to the environment because of brine, which is hot water with a high concentration of salt and other minerals. On average, the production of 1 liter of drinking water induces that of 1.5 L of the concentration NaCl solution from seawater desalination brine (UNESCO report 2019). The main challenge of these stations water desalination plants at the economic level is to control production costs, and at the environmental level is to reduce CO2 emissions and find a solution to solve the brine water problem.

On the other hand, Morocco has a significant hydraulic infrastructure, since there are 149 large dams with a total capacity of over 19 billion cubic meters and 136 small and medium dams in operation, which will allow the Kingdom to improve its water supply, drinking water and irrigation water.

Importance of geoethical approach

A geoethical approach is a major aspect of reducing the demand and use of water by the inhabitants of the research region. Geoethics is a theory of the ethical relationships of man with inorganic nature, based on the perception of inorganic nature as a member of the moral community, a moral partner, and on the principles of equality and equivalence of inorganic matter, as well as the limitations of human rights and needs in relation to inorganic nature (Nikitina 2016; Farahmand et al. 2021). On the basis of this concept, the authorities, scientists and managers involved in the management of groundwater in the Essaouira basin must take into account hydrogeoethical considerations in all of their responsibilities.

The overexploitation of groundwater and intensive irrigation in the main canal controls have posed serious problems for groundwater managers in the Essaouira basin. Depletion of water tables, encroachment of salt water, drying up of aquifers, pollution of water tables, waterlogging and salinity, etc., are major consequences of overexploitation and intensive irrigation.

People should be aware of this fact that the recharge of the Essaouira aquifer is fed only by precipitation (El Mountassir et al. 2021a, 2021d), and is diminishing by the effect of climate change (Bahir et al. 2020), so that they understand the current critical situation of water resources. Government and authorities should develop a geoethical approach including behaviors and values such as commitment, responsibility and humanity regarding ways to protect groundwater from pollution and excessive discharge from school, television, social media, etc.

Conclusion

Nitrate pollution is considered one of the most common environmental problems in groundwater, especially in areas affected by agriculture, such as the semi-arid region of the Essaouira basin. In this study, groundwater samples were taken from the Meskala-krimat sub-basin area to perform a comprehensive water quality analysis during 12 years. On this basis, the quality of the groundwater and the distribution of nitrate pollution were assessed. Reduced groundwater and surface water supply in recent decades due to the effect of climate change resulting in increased water demand due to higher temperatures. In addition, the use of chemical fertilizers agriculture pollutes the groundwater environment, making groundwater quality worse. The following conclusions of the four groundwater collected in (2007, 2017, 2018, and 2019) can be drawn:

  1. 1.

    The projection of the analyzed samples on the Piper diagram reveals that the Ca–Cl, Ca–Mg–Cl, Na–Cl, and Ca–HCO3 facies are the majority of the samples for all campaigns.

  2. 2.

    The groundwater in the Meskala-Krima sub-basin is slightly acidic to marginally alkaline, with high salinity, which is not suitable for human consumption.

  3. 3.

    The groundwater quality assessment based on WHO standard for drinking and irrigation purposes shows that the groundwater in this area is not suitable for direct drinking by humans, but acceptable for agricultural use with high-salinity hazards.

  4. 4.

    The concentration of nitrate in groundwater in the study area is between 2 and 214 mg/L, with an average of 41.1 mg/L. The largest exceeds WHO drinking water limit standard by 4.28 times. It shows that nitrate pollution in groundwater needs to be controlled urgently. The input of a large amount of nitrogen fertilizer in human agricultural activities is the main source of pollution, and at the same time, decrease in precipitation and an increase in temperature accelerate the severity and spread of pollution by encouraging nitrate retention in the superficial sections of the soil and restricting its penetration into the aquifer.

To manage groundwater in the Essaouira Basin, authorities, scientists and managers must include hydrogeoethical issues in all of their responsibilities. Furthermore, establishing a geoethical approach in society can positively impact water use rates and help maintain groundwater balance in the Essaouira basin.