The OriginPro software version 10.0.0.154 (Learning Edition) was used to perform the Piper diagram projection, Gibbs diagrams, multivariate analysis, essentially the Principal Component Analysis (PCA) commonly applied when assessing hydrochemical data, and box plots. The relevant Geographic Information System (GIS) was employed to create thematic maps for exploring the spatial variations of the parameters.

The critical aspects and indicators of water quality are typically employed to derive the WQI, which serves as a comprehensive metric for evaluating the suitability of water for specific uses and identifying any potential risks linked with its consumption. The current investigation employs a methodology that is widely used by scientists all over the world, highlighting the commonality of study approaches (Akter et al., 2016; Satish Kumar et al., 2016; El-Zeiny and Elbeih, 2019; Asadi et al., 2020; Chakravarty and Gupta, 2021; Afshan et al., 2022; Alshehri and Abdelrahman, 2023; Diédhiou et al., 2023). In order to accommodate the specific requirements of local water quality monitoring and evaluation, it is possible for the factors and weightages utilized in the computation of the water quality index to vary from one region to another. This study utilized a method that selected thirteen parameters associated with water quality, such as EC, pH, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃⁻, SO₄²⁻, Cl⁻, NO₃⁻, NO₂⁻ and NH₄⁻ in order to determine the water quality index. For the present investigation, the Water Quality Index (WQI) was computed using the World Health Organization (WHO, 2022) standards presented in Table 2 and the subsequent equations:

Wi defines the weight of each parameter, n is for the number of parameters, wi refers to the relative weight of each parameter. The weight (wi) of each parameter and the resulting relative weight value (Wi) are shown in Supplementary Material: Table 5. Qi represents the quality assessment, Ci is for the concentration of a single physicochemical parameter in each water sample, and Si serves to the WHO drinking water standard for each physicochemical parameter. The pH standard is between 6.5 and 8.5 (WHO, 2022), and the assessment method was thus obtained using the following equation:

The irrigation suitability indicators often used for analyzing water relevance include Sodium Absorption Rate (SAR), Sodium Percent (Na%), Kelly’s Ratio (KR), Magnesium Hazard (MH), and Permeability Index (PI), which have been estimated using the formulas shown in Table 3.

The hydrochemical study reveals that the major ions of the quaternary groundwater are dominated in the following order: Cl⁻>HCO₃⁻>SO₄²⁻>Na⁺>Ca²⁺>Mg²⁺>K⁺>NO₃⁻>NO₂⁻>NH₄⁺. The large range of physicochemical parameter variability shows varying amounts of water salinization and mineralization as illustrated with the box plots (Supplementary Material: Figure 1) that may result from various mechanisms such as natural sources like ion exchange processes between groundwater and geologic strata. As well as the climate of the region which is characterized by high temperatures and a high evaporation rate, palm grove soil lessening (Baki et al., 2016) or anthropogenic sources related to human activities. Piper diagram (Piper, 1944) allows us to estimate the percentage of chemical elements and classify them (Figure 7). The significant proportion of samples obtained throughout the eight sampling campaigns is of mixed Cl-SO₄-Ca-Mg type (67% in the 2000 campaign, 80% in 2004, 83% in 2007, 84.6% in 2009, 72.7% in 2016, 81.8% in 2018, 90.9% in 2020, and 92.3% in 2021). Other samples from the previous campaigns have minor amounts of additional chemical facies such as HCO₃-Ca-Mg, and mixed SO₄-Cl-Na type.

Gibbs diagrams are frequently used to investigate the essential components influencing hydrochemical composition (Gibbs, 1970). The diagram shows three independent domains: zones dominated by precipitation, evaporation, and rock weathering. The Gibbs ratios can be calculated as follows:

The designed ratios versus TDS were used to construct the Gibbs diagrams. The water samples are placed in the upper right zone with high values of TDS and ratio I, indicating that the chemical compositions were influenced by evaporation. Samples with high TDS but low ratio II values, on the other hand, fall in the middle zone, indicating that the rock weathering process is dominant. Based on the findings reported in Figure 8, the majority of the groundwater samples are located in a zone dominated by the evaporation process principally and rock weathering to a minor extent.

The statistics indicate that some physicochemical parameters in some locations do not satisfy the WHO and Moroccan requirements for safe drinking water. However, it has been revealed that the concentration of the parameters in certain samples is within the suggested limits.

The temperature shows a moderate variation from one place to another with a minimum of 16.2°C and a maximum of 26°C in the year 2021. For the other years, the minimum varies from 12°C to 22°C while the maximum is always around 25°C (Figure 9A). The observed temperatures may be comparable to the surface temperature, which is explained by the time of sampling, which was performed during the first hours of the day when temperatures were relatively low in comparison to the climate of the region, where the maximum temperature can reach 38°C. However, the observed temperature did not exceed the recommended 25°C for drinkable water.

The pH ranges from neutral to slightly alkaline, with values ranging from 6.5 to 7.9 (Figure 9B), this interval is relatively constant throughout all years studied. The basic pH is located in the upstream part, while the acidic pH is located in the center of the study zone, and the pH in the downstream part is neutral. There was a minor difference in pH between each sample, which might be explained by the nature of the surrounding rocks crossed. The WHO pH recommendation for drinkable water is between 6.5 and 8, while the Moroccan Standard is between 6.5 and 9. The pH values of all samples are generally within the recommended range.

Electrical Conductivity (EC) defines the levels of soluble salts in the water (Dandge and Patil, 2021; Mahammad et al., 2022). The EC varies significantly across the places examined in the study area (Figure 9C), with a mean of 2957.84 µS/cm (campaign of 2021). The maximum EC value of around 9605 µS/cm (campaign of 2004) was discovered in the Tizougaghine sample, and the lowest value of 699 µS/cm (campaign of 2018) was discovered in the Gardmit sample (Figure 10). In contrast to the other years, the saline charge is decreasing in the campaign samples from 2009, 2016, and 2018. The values range from 699 to 980 µS/cm as minimum and 3111 to 3590 µS/cm as maximum, with the average being 1833 µS/cm. The EC measurements taken at various locations are generally within a range that exceeds the guidelines described in Table 2.

Turbidity is a measure of the clarity or cloudiness of water (Çako et al., 2013). Turbidity can be caused by the movement of specific materials such as sediments, mineral precipitations, and biomass, and its presence can be permanent or seasonal (Nduka et al., 2008). The permissible level for drinking purposes is 5 FNU. The observed turbidity values range from 17.7 to 107.3 FNU with an overall average of 36.94 FNU (Figure 9D). According to Moroccan and WHO standards, all samples have turbidity levels that exceed the maximum tolerable portability limits.

The range of TDS in Tinejdad-Touroug groundwater is 472 to 4416 mg/L, the average is about 1599.6 mg/L. The distribution of high values is closely related to EC, turbidity, and pH values. The highest value is always recorded in Tizougaghine and Igli samples (central part and groundwater’s borders). However, the samples from the margins had low concentrations. The values observed in the TDS spatial distribution map (Figure 9E) clearly show that 82% of samples of the study area contain concentrations overhead of the drinking water guidelines indicated in Table 2.

Dissolved oxygen is a measure of the concentration of available oxygen in water used by microorganisms in the biological oxidation of organic matter. The concentration of oxygen that is dissolved in water can be affected by various factors, including the origin of the water, the temperature of the water, the methods used to treat the water, and the chemical or biological reactions that take place within the distribution system, as stated by the (WHO, 2022). Its value provides information on the degree of contamination and hence the degree of auto-purification of water (Al-Asadi et al., 2020). In this study, oxygen concentrations ranged between 0.5 mg/L and 2 mg/L on average (Figure 9F).

The total hardness of groundwater is caused by the presence of calcium and magnesium ions (Das et al., 2019; Ram et al., 2021), the World Health Organization’s guideline value for TH in drinking water is about 120 mg/L. The TH readings in all locations respect the WHO’s limit. The maximum TH value is observed in Igli sample at about 200 mg/L, and average total hardness levels range from 81.81 mg/L in 2000 to 92.02 mg/L in 2021with an increase of 10.21 mg/L.

Ca concentrations are within the guidelines mentioned in Table 2, with averages ranging from 168.27 mg/L (2000 campaign) to 189.66 mg/L (2021 campaign). Some exceptions are observed for concentrations that do not meet the required standards such as in Melaab sample (385 mg/L, 489 mg/L, 309 mg/L, 206 mg/L, and 371 mg/L consecutively for 2000, 2004, 2007, 2009, and 2021 campaigns).

Mg concentrations for 2004, 2016, and 2018, and more than half of the samples in 2020 are within the allowable range for drinking water with minimum levels ranging from 8.50 to 56.5 mg/L. The campaigns 2000, 2007, 2009, and 2021 show values that exceed 70 mg/L the tolerated limit with maximums that reach 355 mg/L.

Bicarbonate levels in Tinejdad-Touroug differ considerably from 111.02 to 1485 mg/L, with an overall average of 495.06 mg/L. Calcium and magnesium are two essential minerals that can be obtained from various sources. The presence of ferromagnesium minerals in the natural surroundings, dolomite weathering and dissolution of calcite are some of the processes to acquire these essential minerals (Gautam et al., 2022; Goswami et al., 2022; Gugulothu et al., 2022). The Palaeozoic substratum of the Anti-Atlas, as well as the limestone and dolomitic rocks of the Jurassic Mountains in the High-Atlas region, are considered potential sources of calcium and magnesium minerals.

Chloride, a common element, is found in groundwater from various sources, including surrounding rocks, salt is transported through rainwater, seawater intrusion, and pollution caused by domestic sewage and industrial waste (Goswami et al., 2022; Alshehri and Abdelrahman, 2023; Elkhalki et al., 2023). Water that contains a significant amount of chloride tends to emanate an unpleasant odor (Honig et al., 2020). Furthermore, such water also demonstrates heightened levels of electrical conductivity (Solangi et al., 2020). Cl ranges between 79.4 and 1761 mg/L for the 2000 campaign, 76.6 and 1111 mg/L for the 2004 campaign, 123 and 1868 mg/L for the 2007 campaign, 198 and 1163 mg/L for the 2009 campaign, 127.8 and 901.7 mg/L for the 2016 campaign, 89.41 and 721.4 mg/L for the 2018 campaign, 46.15 and 621.3 mg/L for the 2020 campaign and 145.6 and 1527 mg/L for the 2021 campaign (Supplementary Material: Figure 1). The recommended chloride concentration in drinking water is 250 mg/L. Except for specific cases, this water surpasses the 250 mg/L limits for domestic purposes. In our study area, the levels of chloride are commonly associated with a range of geological rocks.

Sulfate refers to a type of salt, a sulfate excess will often add salt to the water and degrade its taste. The high content of sulfate in groundwater might cause dehydration, catharsis, and gastrointestinal problems (Nduka et al., 2008; Qureshi et al., 2021). The WHO recommended value for sulfate is 250 mg/L, although according to Moroccan standards, concentrations as high as 400 mg/L are permitted. Sulfate concentrations are greatest in Igli samples, 1893 mg/L for the 2004 campaign, 1187 mg/L for the 2007 campaign, and 656 mg/L for the 2009 campaign. However, the content of sulfate in water is usually lower than the threshold amount.

Nitrate, which has a considerable impact on agricultural and drinking water usage, has been recognized as the primary groundwater contaminant (Panneerselvam et al., 2023a). The WHO recommends a nitrate concentration of 50 mg/L. The upstream segment of the examined region exhibited considerable levels of nitrates. Furthermore, the levels of nitrates found in the Igli and Tizougaghine samples were higher than in the other specimens. However, the average nitrate content ranges between 27.38 for the 2000 campaign and 31.22 mg/L for the 2021 campaign. The Sat sample found the lowest nitrate content at 0.30 mg/L.

The sodium content is high, ranging from 95 to 670 mg/L. The maximum value was recorded in the central part, the average ranges from 284.04 mg/L in 2000 to 268.64 mg/L in 2021 with a decrease of 15.4 mg/L. Although potassium showed very low values which are within the permissible range for drinking water. Ammonia is a high-level indicator of organic-substance contamination (Wiatkowski and Paul, 2009). The WHO has mandated a limit of 0.5 mg/L for potable water provisioning. All samples in different years controlled are within acceptable limits for potable water purposes.

Microbial indicators may be quantified to determine the amount of organic contamination in groundwater (Szekeres et al., 2018; Hubbard et al., 2020; Khadra et al., 2022; Stupar et al., 2022; Li et al., 2023). The results of bacteriological parameters in the samples obtained throughout five sampling campaigns are moderate. Faecal Coliform ranges between 0 and 400/100ml, 0 and 160/100ml, 0 and 800/100ml, 1 and 248/100ml, and 7 and 44/100ml during 2000, 2004, 2007, 2016, and 2020 campaigns, consecutively. Samples taken during the 2000 campaign ranged between 0 and 800/100ml for Total Coliform and between 0 and 330/100ml for Faecal Spectroscopy.

The studies for the 2004 campaign showed a decrease compared to the previous campaign, with an average of 34.36 instead of 255 for the Faecal Coliform and 15 instead of 43 for the Faecal Spectroscopy. However, analyses for the 2007 campaign indicate an increase, with an average of 340 for Faecal Coliform and 325 for Faecal Spectroscopy. Total Coliform readings for the 2016 campaign ranged from 5 to 298/100ml, with an average of 99/100ml, and for the 2020 campaign ranged from 18 to 102/100ml, with an average of 41/100ml. Faecal Spectroscopy rates range from 1 to 34/100ml, with an average of 6/100ml in the 2016 campaign, and 2 to 22/100ml in the 2020 campaign, with an average of 14/100ml.

The majority of samples indicate null values for the examination of bacteriological parameters for the campaigns 2009, 2018, and 2021, except for a few sampling sites where the values are positive but always remain below the prescribed limits for drinking water.

Horton et al., 1965 and Brown et al., 1970 proposed a water quality index to facilitate water assessment and interpretation. The index is calculated by assigning a weight to each parameter based on its relative contribution to the intended or optimal values. Individual values are then weighted depending on their importance (Supplementary Material: Table 5), and the weighted values are used to generate the overall water quality index. The calculated WQI values are classified into five categories, as indicated in Supplementary Material: Table 6, which vary from “excellent water” to “water unsuitable” for consumption. In general, a higher index implies potentially higher levels of pollution or contamination, however, a lower index suggests improved water quality. Several studies related to the assessment of groundwater quality within the adoption of the WQI have been carried out in Morocco (Bahir et al., 2020; El Mountassir et al., 2020; Jamaa et al., 2020; Bahir et al., 2021a; Bahir et al., 2021b; Sarti et al., 2021; Bahir et al., 2022; Ouhamdouch et al., 2022; Rafik et al., 2022; Benaissa et al., 2023; Boudellah et al., 2023; El Moustaine et al., 2023; El Yousfi et al., 2023).

In the current study, 54.5% of samples from the 2021 campaign had poor quality (class III), with WQI values ranging from 100 to 200, and 27.3% have very poor quality (class IV), with values varying between 207 and 250. Class II and Class V both have one sample, making up 9.1% of the total number of samples (Figure 11A). In the 2020 campaign, 54.5% of samples are categorized as class II, while 45.5% are classified as class III (Figure 11B). For the 2018 campaign, 9.1% of water points are in class I, 36.4% in class II, 45.4% in class III, and one sample in class IV, accounting for 9.1% of total samples (Figure 11C).

For 2016 samples, 10% are regarded as class I, while 90% are classified as class III (Figure 11D). 7.7% of samples in the 2009 campaign were classified as class II, 69.2% as class III, 15.4% as class IV, and 7.7% as class V (Figure 12A). For the 2007 campaign, 50% of water sites occurred in class III, 25% remained in class V, and 16.7% and 8.3% were in class IV and II, respectively (Figure 12B). Class III accounted for 40% of all samples collected during the 2004 campaign, whereas classes II and IV accounted for 40% and 20%, respectively (Figure 12C). Regarding the case of the samples from the 2000 campaign, 58% qualify as class III, 25.4% as class II, and 8.3% as class IV and V (Figure 12D).

The local difference of the WQI metric shows that groundwater quality varies periodically as illustrated in Figures 11, 12, and the variability of the matrix properties of the bedrock in the region examined might explain this discrepancy. The Tizougaghine, Izilf and Igli locations present a very poor quality. This weakness could also be explained by the decreasing thickness of the aquifer towards the boundaries, where the water table is easily attenuated by surface water, and by the region’s rainfall deficit caused by climate change. In fact, the decreasing trend in the piezometric level is followed by an increasing tendency in the EC levels, giving rise to a deterioration of the quality of the groundwater. Nonetheless, groundwater quality in the study region is negatively impacted periodically due to the combined effects of climate change and human activities.

Minerals found in significant amounts in water have negative effects on the soil and plants. As a result, the parameters that define irrigation water must be studied. The evaluation of groundwater waters for agricultural use is being studied using several indicators (Table 3). The results were evaluated using recommended quality standards and classifications determined by the authors who established the index for the first time.