Water quality assessment and hydrochemical characterization of Zamzam groundwater, Saudi Arabia
This study focuses on chemical and microbial analyses of 50 Zamzam water samples, Saudi Arabia. The soluble ions, trace elements, total colony counts, total coliform group, and E. coli were determined and compared with WHO standards. The obtained results indicated that the dissolved salts, soluble cations and anions, Pb, Cd, As, Zn, Cu, Ni, Co, Fe, Mn, Cr, PO4 3−, NO2 −, Br−, F−, NH4 +, and Li+, were within permissible limits for all samples. Yet, 2% of waters contain NO3 − at slightly high concentration. The water quality index (WQI) reveals that 94% of the samples were excellent for drinking (class I). While the remaining was unsuitable due to total coliform group contamination “class (V)”. Durov diagram suggest no clear facies and dominant water type can be noted. It indicates mixing processes of two or more different facies might be occurring in the groundwater system. All studied waters were undersaturated with respect to halite, gypsum, fluorite, and anhydrite. These minerals tend to dissolve and increase water salinity. A direct relationship between Zamzam water salinity and rainfall is recorded. The water salinity fluctuated between 4500 mg L−1 (year 1950) and 500 mg L−1 (year 2015) based on rainfall extent. The approach applied can be used to similar groundwater worldwide.
KeywordsZamzam Groundwater quality Water quality index AquaChem software
It is unnecessary to say that the quality of water is the most significant concerns of human health, especially in arid environment (Al-Omran et al. 2012). Sometime, humans have to use water contaminated by disease vectors, pathogens, or improper concentrations of toxins (William and Frank 2000). Using this water may lead to various diseases and sometimes death. Monitoring drinking groundwater is essential to confirm its safety (USEPA 2007). The hydrochemical and microbial analyses of groundwater have a substantial role in assessing water quality (Tiwari 2011). Countless people drink Zamzam groundwater in Saudi Arabia (Shomar 2012). According to Arab historians, the Zamzam well has been in use for around 4000 years (Khalid et al. 2014). The major solute chemistry reveals that the water contains high concentration of calcium and its water type is calcium carbonate type. The water is alkaline and the distributions of major salts are: magnesium bicarbonate, magnesium sulfate, sodium and potassium chloride (Shomar 2012; Al-Gamal 2009). The long residence time with aquifer materials of basic lava origin (basalt) led to the formation of ferro-magnesium minerals, soluble calcium and magnesium, in water (Al-Gamal 2009). Shomar (2012) reported that the Zamzam water contains high concentration of As and NO3 and set above permission limit of WHO; on the other hand, Al Nouri et al. (2014) reported that the Zamzam water is free of As contaminations and its concentration sets within permissible limits according to WHO (2011) and SASO (1984). Griffin et al. (2007) reported that the Zamzam water contains high concentration of Fluoride and some other element. Mashat (2010) reported that the Zamzam water has no sign of biological growth due to it is naturally pure and salt-sterilized contents. In 1971, the ministry of agriculture and water resources sent Zamzam water samples to the European laboratories to test its potability. The results indicated that the water can be considered suitable for drinking; nevertheless, it contains slightly high concentration of fluoride, calcium, and magnesium (The annual report of the ministry of agriculture and water resources 1971). Calcium and magnesium in water and food are known to have antitoxic activity. They can help prevent the absorption of some toxic elements such as lead and cadmium from the intestine into the blood, either via direct reaction leading to formation of a non-absorbable compound or via competition for binding sites (Kozisek 2004). In addition, the WHO (1980) concluded that the populations supplied with low-mineral water may be at a higher risk in terms of adverse effects from exposure to toxic substances compared to populations supplied with water containing adequate mineral and hardness. Furthermore, the low mineral water and low TDS may cause salts to be leached from the human body. Shomar (2012) reported that the top 14 m of the Zamzam well is excavated in the sandy alluvium of the Wadi Ibrahim; however, the lower 17 m is located in the diorite bedrock. A 0.5-m-thick highly permeable weathered rock located between the alluvium and bedrock was observed. Most of the alluvial section of the well is lined with stone except for the uppermost 1 m, which has a reinforced concrete collar. The water enters to Zamzam well from alluvial section and at depth 13 m from surface. In attempting to test the well flow rate, a pumping machine at 8000 L s−1 was operated for more than 24 h. This test showed a decrease in the level of water by about 10 m and then the water level stopped receding. The water level recovered to its approximately original surface just after 11 min after pumping had stopped (ZSRC 2011). The aquifer feeding the Zamzam well appears to recharge from rock fractures in adjacent mountains around Mecca (Makkah). Therefore, the well taps groundwater primarily from the spring-fed alluvium and to a lesser extent from water percolating up through the permeable, weathered fresh bedrock (ZSRC 2011). This study aims to investigate the chemical and microbiological composition of Zamzam water, assess Zamzam waters for drinking purposes, and finally classify the hydrochemical characterization of Zamzam well.
Materials and methods
Chemical and microbiological analysis
Fifty water samples were collected from different locations in Saudi Arabia (Supplementary Table 1). Three samples were collected from the original well in Mecca, 13 samples from taps connected to the original well, ten samples from ice box filled with Zamzam water inside and outside Alharam in Mecca, three samples from Zamzam bottled Water Company in Mecca, 15 samples from Al-Madenah Almonawara, and six samples from Riyadh city. The Zamzam waters of Al-Madenah were transported from Mecca by government; however, Riyadh Zamzam waters were transported from bottled water company in Mecca by traders and sold in supermarkets and food stores in Riyadh. All samples were gathered, stored in ice box, and transported to King Saud University labs for analyses.
Several microbiological estimations were conducted in this study, including the total colony counts, total coliform group, and E. coli. The total numbers of colony were determined by nutrient agar method; however, the coliform group and E. coli were determined by Colilert (defined substrate) method as described by Eckner (1998) and Maheux et al. (2008).
The water electrical conductivity (EC) in dS m−1 was measured using EC meter at 25 °C (Test kit Model 1500-20, Cole and Parmer); however, the pH was measured by pH meters (CG 817) (APHA 1998). In Addition, calcium (Ca2+), magnesium (Mg2+), sodium (Na+), lithium (Li+), potassium (K+), ammonium (NH4 +), fluoride (F−), bromide (Br−), chloride (Cl−), sulfate (SO4 2−), phosphate (PO4 3−), nitrate (NO3 −), and nitrite (NO2 −) were determined using ion chromatography system (ICS 5000, Thermo (USA)). The arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) were measured using ICP-Perkin Elmer Model 4300DV. Furthermore, carbonate (CO3 2−) and bicarbonate (HCO3 −) were determined by titration with sulfuric acid (H2SO4) (Matiti 2004).
Standards and chemicals
Dionex combined cation standard and anion standard solutions and PerkinElmer quality control multi-element standards were purchased and used as a stock standard for preparing working standards of ICS and ICP, respectively. All solutions were stored in precleaned high-density polyethylene (HDPE) bottles and refrigerated at 4 °C. The working standards were prepared by serial volume/volume dilution in polypropylene vials (Sarstedt, Germany). Micropipettes (Eppendorf, Sigma-Aldrich) with disposable tips were used for pipetting all solutions. High-purity water (18.2 MΩ) was prepared using a Millipore ion-exchange system fed with deionized water (US filter).
Ion balance errors
Water quality indices computing
The water quality index (WQI) calculations include three sequential steps as in Yidana and Yidana (2010), Al-hadithi (2012) and Aly et al. (2015). In this study, minor modification was performed when water contains coliform group and/or E. coli. The water is classified directly without calculation to be unsuitable for drinking (Al-Omran et al. 2015).
The first step is ‘assigning weight’: each of the 13 parameters, with exception coliform group and/or E. coli, has been assigned a weight (wi), according to its relative importance in the overall drinking water quality as shown in Supplementary Table 2. The most significant parameters gave a weight of 5 and the least significant gave a weight of 1. The coliform group and E. coli gave no weight; however, the water quality changed directly to class V (water unsuitable for drinking). In this study, the maximum weight of 5 referred to As, Cd, Pb, NO3, NO2, and total counts; due to its adverse effect on water quality assessment (Ramakrishnalah et al. 2009), the less harmful elements, i.e., Fe, Zn, and Mn have been given a weight of 1.
The hydrochemical characterization of the groundwater samples was evaluated by means of major ions, Ca2+, Mg2+, Na+, K+, HCO3 −, Cl−, and SO4 2−. The chemical analysis data of the water samples were plotted on the Piper, Schoeller, and Durov diagrams using Geochemistry Software AquaChem 2014.2 for the identification of water types.
The hydro-geochemical equilibrium model, Phreeqc model (Parkhurst and Appelo 1999), was used to calculate the SI of the groundwater with respect to the main mineral phases.
Results and discussion
Long-term Zamzam water salinity and rainfall monitoring
Water quality assessment for drinking purpose
The results of this study showed that all studied Zamzam waters were free of E. coli contamination; moreover, the total colony counts (CFU) fall within the permissible limits for all samples. The USEPA (2009) allow microbial load of 500 CFU/mL; on the other hand, no cell of E. coli permit. Three water samples (6%) were found unsuitable due to total coliform contamination. The total coliform groups in the three samples were 689.6, 1986.3, and 1102 (CFU/100 mL); nevertheless, the remaining (94%) have no total coliforms. The samples collected from the main sources were found free of this contamination; consequently, this contamination is caused by an external source as a result of unacceptable human behavior (Al-Omran et al. 2015; Al-Barakah et al. 2016) (Supplementary Table 1).
The groundwater’s maximum (max), minimum (min), and standard deviation (SD) of the measured parameters was conducted to find out the parameters which differs from the drinking water standards derived by WHO (2011). It was found that the maximum values of most chemical parameters in the studied water were within the permissible limits of the used standard (Al-Omran et al. 2012; Aly et al. 2013). Only one water sample, (the 2% of the water samples) contains nitrate concentration (52.8 mg L−1) which slightly exceeds the limits given by the literature (WHO 2011; USEPA 2009). Although this study suggests that the Zamzam water salinity was within acceptable limit, most groundwaters in Saudi Arabia are characterized by high salinity (Al-Omran et al. 2012; Aly et al. 2013). The studied groundwater’s EC ranged between 0.77 and 0.83 dS m−1 (SD = ±0.14); however, the pH lies in between 7.81 and 8.45 (SD = ±0.14). The max, min, and (SD) values of Ca2+, Mg2+, Na+, K+, CO3 2−, HCO3 −, Cl−, and SO4 2− were 2.82–3.78 (±0.19), 1.90–2.64 (±0.14), 2.92–3.98 (±0.21), 0.39–0.70 (±0.04), 0.00–1.60 (±0.04), 2.20–4.10 (±0.35), 2.86–3.86 (±0.13), and 2.35–2.94 (±0.07) meq L−1, respectively. Furthermore, the max and min concentrations, and (SD) of Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Pb, PO4 3−, NO3 −, NO2 −, Br−, F−, NH4 +, and Li+ were 0.092–7.450 (±1.121), 0.028–0.632 (±0.131), 58.476–72.097 (±3.314), 0.009–0.414 (±0.046), 0.729–2.149 (±0.375), 1.687–9.717 (±1.083), 0.000–17.900 (±3.390), 0.006–7.728 (±1.621), 0.040–0.113 (±0.012), 0.000–0.385 (±0.078), 0.000–0.107 (±0.25), 30.00–52.79 (±3.52), 0.00–3.03 (±0.471), 0.230–0.685 (±0.057), 0.780–1.590 (±0.100), 0.000–2.489 (±0.624), and 0.010–0.243 (±0.069) μg L−1, respectively. The average Li+ concentration found in water was 0.184 mg L−1. The Li+ is considered a valuable elements when presence in drinking water since it reduced the incidence rates of suicide, homicide, and rape (Schrauzer and Shrestha 1990; Ohgami et al. 2009; Al-Barakah et al. 2016). F− was also found in high concentrations in studied water samples and set within the recommended level of WHO (2011) standard. The mean value of F− in the water is 0.9 mg L−1.
Drinking water quality index
Salinity and alkalinity hazard class Irrigation
The saturation index (SI) is the parameter generally used for groundwater. Water is in equilibrium with a mineral when the SI = zero. It is under-saturated if the SI < zero and it is over-saturated when the SI > zero. Nonetheless, to overcome the measurement inaccuracies and changes in the water composition when it makes its way towards the surface, it is proposed to consider a wider range of SI, such as −1 < SI < +1 (Aly 2015).
In this study, a direct relationship between Zamzam groundwater salinity and rainfall is recorded. The distribution of chemical and microbial constituents of the waters were determined and compared with WHO drinking water quality standard. Furthermore, the water quality index (WQI), a mathematical method used to facilitate water quality explanation, was also calculated. The results revealed that the water lies within acceptable limits with respect to dissolved salts, soluble cations and anions, Pb, Cd, As, Zn, Cu, Ni, Co, Fe, Mn, Cr, PO4 3−, NO2 −, Br−, F−, NH4 +, and Li+. The nitrate contents of only a small proportion (2%) of the water samples were slightly exceeded the corresponding permissible limits. The computed WQI values reveal that 94% of the water samples were excellent for drinking (class I), and its WQIs were ranged between 28 and 41 with an average of 31. The remaining water samples were considered unsuitable for drinking “class (V)” due to microbial contamination by total coliforms. The chemical data of the water samples were plotted on Piper, Schoeller, Durov, and Gibbs diagrams. The results concluded that the main water types of the studied well are the following: Ca2+–Mg2+/SO4 2−–Cl−. The Schoeller diagram reveals that there is a prevalence of Ca2+ and Na+ which influences the affinities to the HCO3 −, Cl−, and SO4 2−. The Durov’s diagram demonstrates that there are mixing processes of two or more different facies that might be occurring in groundwater system. The distribution of samples in Gibbs’s diagrams suggests that the chemical weathering of rock-forming minerals is influencing the groundwater quality. The SI indicated that all investigated waters are undersaturated with respect to halite, gypsum, fluorite, and anhydrite. However, they are saturated with respect to dolomite, calcite, and aragonite. Consequently, the undersaturated minerals tend to dissolve and there is an opportunity for more Na+, Ca2+, Cl−, F, and SO4 2−concentration increase in the groundwater.
The authors wish to thank King Saud University, Deanship of Scientific Research, College of Food and Agriculture Science, Research Center for supporting the research work.
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