1 Introduction

Many factors affect the water quality index (W.Q.I.), including population growth rate, climate change, and expanded industrial and agriculture activities, which caused a significant decrease in quality of water, which represented a local and global challenge (Krishan et al., 2016). Various physical and chemical variables were adopted by researchers to evaluate the W.Q.I. for drinking uses. Walsh and Wheeler, (2012) illustrated that multiple factors should be considered when analyzing the water body’s quality. The physicochemical variables relate to the level of abundance of water. Also, the concentrations of variables in the water body significantly affect evaluating the W.Q.I. Furthermore, studying these variables one-variable-at-a-time does not show a comprehensive vision for the W.Q.I. Moreover, water treatment is required if the variables do not meet the region’s standards (Bouderbala, 2017).

Numerical or mathematical methods can calculate the W.Q.I. for drinking uses. These methods can give a broad view of the groundwater quality in a specific area timelessly and effortlessly and, therefore, avoid wells in areas where groundwater is unsuitable to use (Alobaidy et al., 2010). Water source characteristics directly affect groundwater quality and its utilization suitability. Continuous monitoring of the chemical and physical parameters should be maintained and controlled to keep the groundwater quality in a good state to be used.

Recently, the water shortage crisis started to arise in Iraq due to climate change, construction of dams upriver, wars, and unsystematic drinking water use. This shortage raised the need to invest in groundwater resources. Thus, quality analysis is required to check its suitability for use. GIS is highly capable of creating wells’ distribution maps using relevant variables. These maps help specialists cross-examine water quality across multiple sites (Chabuk et al., 2020).

The groundwater quality index method is the most widespread method for assessing water quality in developing countries to maintain water quality. It represents an essential storage strategy for countries’ future uses when decreasing the surface water level. It is a permanent source for groundwater research as it is one of Iraq’s most critical natural resources. The suitability of groundwater in the city of Hillah for the different uses was studied for construction purposes mainly. The groundwater level fluctuations as well as its chemical composition at Hilla city was carefully considered. Two negative influences have a combined effect on concept tolerance. All tested samples for the groundwater showed that they are not suitable for domestic, animal as well as some industrial purposes.

Chabuk et al., (2020) evaluated the groundwater for irrigation in Al-Hillah city by applying the water quality index for the irrigation model (WQIIR) in the GIS environment. They measured Ca, Mg, Cl, EC, HCO3, Na, and SAR in 48 wells distributed in different areas in Al-Hillah city. The results based on the predicted maps in 2016

showed that the values of areas in 2016 were about 48.4 km2, 399 km2, 384.3 km2, 28.1 km2, and 0.2 km2. These categories were classified for irrigation (respectively) as a severe restriction, high restriction, moderate restriction, low restriction, and no restriction.

The W.Q.I. method was applied to evaluate the groundwater quality by many researchers in various study areas. Alikhan et al., (2020) estimated the groundwater quality at five wells in Al Najaf city, Iraq, in 2017 using nine parameters (pH, EC, TDS, Ca, Mg, Cl, Na, K, and SO4). The study found that the total value of the W.Q.I. was classed under a poor rating.

Mohammed et al., (2020) adopted the W.Q.I. method to evaluate groundwater quality in the Domiz refugee camp, Duhok governorate. Twenty-four variables were measured in 8 wells. The results showed that the W.Q.I. values were rated as very poor in well 1; poor in wells 2 and 3; good in wells 4, 6, and 7; and excellent in wells 5 and 8.

Othman and Ibrahim, (2021) studied the quality of groundwater for drinking and other domestic uses and the activities of agriculture in Erbil city, Iraq, using the Canadian method for water quality index. They measured twenty-two variables in 16 wells in December/2016, and during the three months of March, June, and September/2017. These variables are pH, EC, TH, Ca, Mg, alkalinity, Cl, DO, BOD5, Na, K, SO4, PO4, NO3, oil and grease, Zn, Cu, Fe, Ni, Pb, Cd, and Hg. The results showed that the total value of W.Q.I. was 38.9, which classified the groundwater quality in the study area as poor quality.

The purpose of creating a new map of groundwater for drinking uses is that the study zone does not have a map for groundwater. The study zone has been affected by the global warming problem which led to searching for another way to cover the shortage. The map will be a document to help the researchers and the specialists. Also, the future plan for the Governorate is to secure additional drinking water sources when necessary and help with future suburbs of the city. Moreover, the map is an easy way to show the groundwater to users.

The research is interested in studying the suitability of the groundwater in Al-Hillah city for drinking and household uses by measuring the available variables within 56 wells from various areas. This study aims to create the prediction map using the groundwater quality index model for drinking uses (GW.Q.I.). Then, the values of GW.Q.I. will enter within the interpolation technique IDW in the GIS to produce the prediction map.

2 Methodology

2.1 Study Area

Al-Hillah city is situated between latitude 32° 29′ 00" N and longitude 44° 26′ 00". Al-Hillah city represents the capital of Babylon Governorate. Al-Hillah city includes three major cities: Al-Hillah center, Abi-Ghraq, and Al-Kifll (Fig. 1).

Fig. 1
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Map of the study area showing the sampling sites

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Al-Hillah city is situated in an arid region and its area of 860 km2. According to the Iraqi Ministry of Planning, (2017)Al-Hillah city has a population of nearly 993,000 inhabitants in 2020. The climate of Al-Hillah city is fluctuating seasonally and daily. The average speed of wind is 7.2 km/h year. The average annual rainfall in this area is about 100 mm, with an average annual relative humidity of 45%. The temperature is changing from more than 50 °C during the summer to over 0 °C during the winter (Iraqi Ministry of transportation constitutions, 2019).

The hydrogeology of Al-Hillah city, Babylon Governorate, is situated in the middle of Iraq in the aquifer of Mesopotamia zone (MZ) in a large flat plain (Al-Madhlom et al., 2020; Sissakian, 2013). The elevation of MZ ranges between 1 and 200 m above mean sea level (a.m.s.l.). The Mesopotamia region is covered mainly by the Quaternary sediments (Al-Madhlom et al., 2020). Al-Hillah city is positioned within the Mesopotamia plan silt zone covered by the Holocene Sequence with a thickness of about 20 m. Its primary compositions are silty clay, loamy sand, and sandy loam soil (Tyagi et al., 2013). The groundwater in the study area is shallow with ranges of 0.4–4.5 m (Chabuk et al., 2021) (Fig. 2) and flows with the trend of surface drainage from northwest to southeast (Al-Jiburi & Al-Basrawi, 2011).

Fig. 2
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Groundwater depths throughout Al-Hillah city (Chabuk et al., 2021)

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The groundwater level rises during the winter and spring season due to increased rainfall and reduction in evaporation. The type of groundwater varies from sulfate to chloride based on the groundwater level and the quantity of recharge by runoff from discharge areas (Al-Jiburi & Al-Basrawi, 2011). In general, the groundwater, located near/around the surface water, has a good quality for use.

2.2 Prediction Maps in GIS Using the Interpolation Method (IDW)

To generate the interpolation map of the groundwater quality index for drinking uses for each variable, the interpolation inverse distance weighted technique (IDWT) was applied in the GIS. The interpolation method is used to estimate the unidentified point at a specific position based on the values of defined points near the unidentified points. The spatial interpolation technique is applied to produce interpolation maps of groundwater quality rather than other techniques (e.g., Kriging, Topo to Raster). The IDW technique gave better and more accurate results than other spatial ones, according to Abbas, (2013).

The IDWT is determined using Eq. (1) (Panhalkar & Jarag, 2016) as follows:

$${SE}_0=\frac{\sum_{i=1}^nN_i\frac1{D_i^p}}{\sum_{i=1}^n\frac1{D_i^p}}$$
(1)

where SE0 is the estimated value of unidentified points; Ni is the value of the defined point; Di is the distance between SE0 and Ni; n is the number of Ni entered in the estimation process; ans p is the power value ≥ 1.

2.3 Method of Calculating Weights of Groundwater Quality Index for Drinking Uses

In this research, the weighted arithmetic method is employed to calculate the groundwater quality index for drinking uses. Twelve variables were used for the selected fifty-six wells within Al-Hillah city because the chosen variables are very significant to calculate the water quality index for different purposes. The groundwater quality index for drinking uses for selected wells in Al-Hillah city was calculated using the following Eqs. (2–4) (Tyagi et al., 2013):

$${Su-I}_{i}\left(\frac{{C}_{i}-{C}_{o}}{{ST}_{i}-{C}_{o}}\right)\times 100$$
(2)
$${\mathrm{IW}}_{\mathrm{i}}=\frac{1}{{\mathrm{STV}}_{\mathrm{i}}}$$
(3)
$$\mathrm{GW}.\mathrm{Q}.\mathrm{I}=\frac{\sum \mathrm{SUIi }\times \mathrm{ IWi}}{\sum \mathrm{IWi}}$$
(4)

where Su-Ii is the sub-index of the ith variable, IWi is the inverse weight of the standard value (STVi) of the ith variable, STVi is the standard value of the ith variable (WHO, 2017), Ci is the measured concentration value for the ith variable, Co is the ideal value for each variable in water that has zero value, excluding the pH value which is equal to 7.

For each well within Al-Hillah city, the water quality rating (GW.Q.R.) was given the deserve classification based on the category of the GW.Q.I. according to Alsaqqar et al., (2015) and Ali, (2017) (see Table 1).

Table 1 Classification of G.W.Q.R. based on values of GW.Q.I. (Ali, 2017; Alsaqqar et al., 2015)
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The steps of calculating the GW.Q.I. for drinking uses for each variable can be seen in Table 2. The reading of the measured variables from sixty-five wells in Al-Hillah city in 2018 is shown in Table 3 (Iraqi Ministry of Water Resources, 2017).

Table 2 Calculating of groundwater quality index for drinking uses for each variable
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Table 3 Concentrations of GW in 56 wells in Al-Hillah city (Iraqi Ministry of Water Resources, 2017)
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3 Results and Discussion

This part is divided into three sections depending on the methodology approach. These sections evaluate the concentration values of variables measured in the selected wells, calculating the groundwater quality index for drinking uses for each well in the study area, and creating the maps of the GW.Q.I. and GW.Q.R. for the whole Al-Hillah city using the GIS.

3.1 Prediction Maps for Variables of Groundwater

In the current study, the prediction maps for twelve physicochemical variables measured from the network of wells distributed throughout Al-Hillah city were produced. Fifty-six wells were used to generate prediction maps using the interpolation method in the ArcGIS (10.5) software.

For the chosen variables of groundwater in the study area, the prediction maps for the sodium (Na), total dissolved solids (TDS), electrical conductivity (EC), chloride (Cl), bicarbonates (HCO3−1) sulfates (SO4), calcium (Ca), magnesium (Mg), nitrate (NO3), potassium (K), and pH can be seen in Figs. 3 and 4.

Fig. 3
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Interpolation maps using IDW method in GIS of a Na; b TDS; c EC; d Cl; e HCO3; and f SO4

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Fig. 4
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Interpolation maps using IDW method in GIS of a Ca; b Mg; c NO3; d K; and e pH

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In Fig. 3a, b, c and d, the range values of Na, TDS, EC, and Cl that resulted from the interpolation maps using the IDW method in GIS were (respectively) 41–10,500 mg/l, 401–39,802 mg/l, 631–46,907 µmhos/cm, and 45–14,577 mg/l. For the variables of Na and Cl, category-1 with ranges of 41–2100 mg/l and 45–2900 mg/l covered the big area of the total study area of 93% and 96% respectively. The ranges of 400–8000 mg/l for TDS and 631–9500 for EC represented the most distribution values in the study area (see Fig. 3b and c).

The variable concentrations of HCO3 and SO4, distributed throughout the Al-Hillah city after interpolation within their maps ranged from 83 to 2019 mg/l, and from 66 to 11,531 mg/l, respectively, are shown in Fig. 3e and f. The range of 83–400 mg/l for HCO3 concentration was comprised 81% of the entire area, while 84% of the range of 66–2300 mg/l distributed throughout the prediction map of Al-Hillah city for SO4 concentration.

The readings of variable concentrations Ca, Mg NO3, and K were ranged between 24 and 3078 mg/l, 14 and 1801 mg/l, 0 and 209 mg/l, and 0 and 109 mg/l, respectively. These variables were distributed throughout the study area after interpolation for the readings of 56 wells. Figure 4a, b, c and d shows that the category-1 with ranges (mg/l) of 24–600, 14–360, 0–41.6, and 0–38.8 covered higher percentage of the study area 94% (Ca), 92% (Mg), 95% (NO3), and 97% (K). The range of the predicted map of pH that was divided into five categories was 6.3–8.7. The ranges of 7.26–7.74 and 7.74–8.22 represented together 95% of the total area (Fig. 4e).

The proportion areas of each category for the produced maps for eleven variables (Na, TDS, EC, Cl, HCO3, SO4, Ca, Mg, NO3, K, and pH) can be seen in Table 4.

Table 4 Area of each category for produced maps of the selected variables
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3.2 Groundwater Quality Index for Drinking Uses (GW.Q.I.)

The groundwater quality index for drinking uses was calculated using the method of weighted arithmetic at the selected wells based on Eqs. (2, 3, 4). The GW.Q.I. values for the selected wells were calculated using the weighted arithmetic method (Table 1). All the parameters applied in this study are presented in Table 3 and were significant in this classification for the groundwater quality index. The GW.Q.I. values were classified based on the values of variables measured in the selected wells, as shown in Table 5. The sign of “ × ” referred to that put reading of variable in Table 5 over allowable standards limit, while the word “OK” meant this value of reading within the allowable limit. For instance, the groundwater quality index for drinking uses for well 5 was 82.3 and rated as good because the measured variables of HCO3, NO3, K, and pH were within the standards limit. These variables have significant effects on the value of the GW.Q.I. For well 2, all measured variables except NO3 and pH were over the standards limit; therefore, the value of the GW.Q.I. was 483.7 and rated as very contaminated for drinking uses. The value of the GW.Q.I. in well 48 was 32.1, and it was classified as excellent for drinking uses because all measured readings of variables were within the standards limit. Table 5 shows that most values of the TDS, EC, and Cl were higher than the allowable limit. These values indicated the groundwater in the study area was salinity. All readings of pH measured in the selected wells were the standard limit of 6.5–8.5.

Table 5 Classification of GW.Q.I. for drinking uses; the variables’ values within the allowable limit
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Table 6 shows the values of the groundwater quality index for the variables of Na, TDS, EC, Cl, SO4, Ca, and Mg which were (respectively) 553.2, 1207.7, 867.6, 579.8, 692.9, 446.4, and 462.1 and they classified as very contaminated rating (Vc-GW). The variables HCO3 and K were rated as poor (P-GW) based on their values of groundwater quality index of 176.2 and 118.2, respectively, while NO3 and pH were rated as good (G-GW) and excellent (E) for drinking uses depending on the GW.Q.I. values of 99.4 and 17.8, respectively. The average value of the GW.Q.I. for the selected wells was 177, and the groundwater quality in Al-Hillah city was rated as poor for drinking uses.

Table 6 Values of the GW.Q.I. for drinking uses for each variable and its rating
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3.3 Producing of Distribution Map of Groundwater for Drinking Uses

For Al-Hillah city, the distribution map of groundwater for drinking uses using the GW.Q.I. method can be seen in Fig. 5. Then, based on the GW.Q.I. values, Fig. 6 shows the distribution map of groundwater rating for drinking.

Fig. 5
figure 5

Distributing map of GW.Q.I. for drinking uses of the Al-Hillah city, Babylon, Iraq

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Fig. 6
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Distributing map of GW.Q.R. for drinking uses in the Al-Hillah city, Iraq

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Areas and their proportions of GW.Q.I. and GW.Q.R. in Al-Hillah city that resulted from Figs. 5 and 6 can be seen in Table 7. The values of valid areas that can be used for drinking and other uses cover 126.8 km2 (14.75%) of the entire area of Al-Hillah city 860 km2, which were rated as excellent and good. Otherwise, about 7% of the total areas were considered unacceptable for drinking uses, rated as contaminated and very contaminated.

Table 7 Areas and their proportions of GW.Q.I. and GW.Q.R. in Al-Hillah city
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4 Conclusion

This study has been set to rate the groundwater quality for drinking uses. It is interesting to study the groundwater employed to use in several daily uses that will be extracted from wells distributed in different areas in Al-Hillah city. Therefore, the groundwater quality index model was applied to determine groundwater quality and its suitability for drinking before use by humans. A comparison has been done for the groundwater in the study area with the local groundwater and international standards.

The distribution maps for groundwater have been established using the groundwater quality index for drinking uses and entered into the GIS for this purpose. The produced maps will ease researchers and scientists to determine the quality of groundwater and help them know its ranges and distribution in the study area. The IDW method and the GIS were combined to produce interpolation maps for groundwater quality for drinking uses using twelve variables measured in 56 wells within Al-Hillah city.

The twelve variables entered in the weighted arithmetic method to calculate the groundwater quality index for drinking uses are Ca, Mg, Na, k, C, SO4, HCO3, TH, TDS, NO3, and EC. Based on the GW.Q.I. values, the generated map of groundwater quality was rated into six categories ranging from excellent to very contaminated.

For each variable, the prediction map was produced as a distribution map to cover the whole study area by using the prediction method IDW as a tool existing in the GIS.

The results showed that the generated map for the groundwater quality index in Al-Hillah city was classified and rated into six categories for drinking uses. These categories were occupied (in km2) 5.1, 121.7, 609.9, 63.4, 35.9, and 24.0 km2 with a rating of excellent, good, poor, very poor, contaminated, and very contaminated, respectively. For the selected wells, the average value of the groundwater quality index for drinking uses in Al-Hillah city was about 177; consequently, it was classified as poor water (P-GW) for drinking uses.

In general, the new map of the groundwater classification is significant for future works. These maps provide valuable information on the groundwater status at each well in the study area using some physical and chemical variables. It can be a new guide for academic, agricultural, and industrial specialists.