A comparative study of various parameters of drinking water quality in Shahroud city, Iran: tap water, well water and bottled water

Available freshwater resources account for less than 1% of the total water resources of the world (Cooper & Hiscock, 2019). It is anticipated that by the year 2050, two-thirds of the world's population will live in areas with low access to freshwater resources, and by 2100, this figure may touch 11.2 billion (Biswas & Tortajada, 2019; Ridzuan, 2021). Currently, many countries in the world are grappling with problems of water stress, water scarcity and poor drinking water quality (Biswas & Tortajada, 2019; Hourieh Fallah et al., 2020; Javid et al., 2020a). Accordingly, with an improvement in the general health conditions of the people on account of rapid technological advancements in the field of medicine, the need for an evaluation of the quality of various available drinking water resources, including well water, tap water, and even bottled water, may be necessary, especially in developing countries (van der Linden, 2015; Hourieh Fallah et al., 2020; Javid et al., 2020b; Ghanbarian et al., 2021).

Following numerous reports about the detection of some chemical and microbiological pollutants in well water and even treated tap water, the consumption of bottled water is increasing on a daily basis (Rani & Prasad, 2012; van der Linden, 2015; Brei, 2018). Moreover, the chemical parameters of bottled water such as fluoride, calcium, magnesium, sodium and other additives are almost evident and visible for the consumer (Javid et al., 2020b; Ghanbarian et al., 2021). Hence, the consumption of bottled water as a reliable source of water is increasing day by day around the world.

For example, the consumption of bottled water in Italy in the year 2017, which is the leading market for bottled water, was about 188 L per person per day. In Germany, the second largest consumer of bottled water, it was 175 L per person per day. Moreover, the global average per capita consumption of bottled water stands at 82 L per person per day (Abtahi et al., 2019).

Although manufacturers producing bottled water follow strict quality requirements, some studies have demonstrated that the chemical, physical and microbiological properties of some bottled water brands do not match national and international standards, especially in developing countries. For example, Momtaz et al. (2013) investigated the microbiological quality of tap water and five brands of bottled water in Iran. Based on their analysis, 2.63% of bottled water was infected with Escherichia coli. A study conducted by Shams et al. (2012) for the evaluation of bottled water quality in Gonabad province of Iran showed that the time and storage conditions of bottled water affected its bacteriological quality and reduced water quality. Ehya & Ghanavati (2019) investigated the case of a bottled water distribution in Kohgiluyeh and Boyer-Ahmad Province of Iran and reported that the concentration of calcium, magnesium, sodium and potassium minerals in the bottled water was not at the standard level required for daily supply of these minerals via water.

Against this background, the aim of the present study is to evaluate the chemical and microbiological properties of three forms of drinking water supply used by the residents of Shahroud city. Shahroud is one of the cities of Semnan Province, located in northern Iran, which is surrounded by very different climates. The population of Shahroud was estimated to be 150,129 people in 2016. Water supply in some rural areas of Shahroud is in the form of well water, including 22 wells that are scattered in various parts of the province, with pretreatment via chlorination. However, in urban areas, treated tap water and bottled water are the main forms of drinking water supply. Some physicochemical parameters including electrical conductivity (EC), pH, total dissolved solids (TDSs), fluoride, chloride, turbidity, nitrite, nitrate and total hardness are measured for each supply. Moreover, the microbiological quality is identified using the standard most probable number (MPN) experiments.

Sampling was performed as follows:

• Bottled water: The 10 most widely used brands of bottled water were purchased from supermarkets as samples and transferred to the laboratory for analysis.

• Tap water: Sampling was carried out in 10 sites of the city by considering the distribution of water valves.

• Well water: The samples were collected from 22 water supply wells of Shahroud in four seasons and, by preserving standard conditions of the sample transfer, they were transferred to the laboratory for experiments. Figure 1 shows the geographical location of the sampling points of well water of Shahroud.

The water samples were analyzed on the basis of the procedure given in standard methods for the examination of water and wastewater (APHA) (APHA, AWWA, WEF, 2012). The selected samples were kept in an ice box at 4 °C and then transferred to the laboratory. Microbial experiments were performed in a clean laboratory room. All glass containers and other instruments in contact with the samples were completely cleansed with nitric acid and deionized water.

Some physicochemical parameters including EC, pH, TDSs, fluoride, chloride, turbidity, nitrite, nitrate and total hardness were examined for sampling the water. These parameters were chosen on the basis of their importance in water resources and specified on the labels of bottles. Hardness was determined by the standard titration method and pH was measured by using the pH meter (model PL-700PV). EC and TDSs were measured by using the TDS meter (model AZ8361). EC, TDS and pH were assessed at the sampling site. Turbidity was measured by using the turbidity meter (model AL250T-IR). Chlorine concentration was evaluated by the Mohr method. Fluoride was measured by the SPADNS method. Nitrite and nitrate were assessed by the standard colorimetric method using a spectrophotometer (Lambda 365 UV/Vis, Perkin Elmer). Moreover, microbial tests were performed using the MPN method. All chemicals used in this study were of high analytical grade and were obtained from the Merck Company. The concentration of dissolved solids, fluoride, chloride, nitrite, nitrate and hardness were reported as mg/L. EC was reported as μmho/cm and the number of coliforms was reported as count per 100 mL.

All experiments were performed in triplicate and the results were reported as the mean value ± SD (standard deviation). The obtained data were analyzed using Prism 2007 software, and analysis of variance (ANOVA) was used to determine the statistical significant difference between the physical, chemical and microbial quality of the three water groups. The Student–Newman–Keuls (SNK) test was used to investigate the significance of the mean difference between every two water groups. The measured values of each parameter were compared with the desired values in the instructions and standards for drinking water developed by the WHO, Institute of Standards and Industrial Research of Iran (ISIRI) and the International Bottled Water Association (IBWA), and these are represented in Table 1.

Table 2 presents the selected physical, chemical and microbial parameters of sampled well water. Moreover, the minimum, maximum, mean and SD of each measured parameter were also represented. Accordingly, the quality of the well water of Shahroud was compared with the ISIRI and WHO guidelines.

The mean values of physical, chemical and microbial parameters in the tap water samples are presented in Table 3 and compared with the ISIRI and WHO guidelines. Moreover, the minimum, maximum, mean and SD of each parameter were assessed.

By comparing the quality of parameters evaluated in the water supply resources (wells) of Shahroud and the quality of water at the point-of-use, it was revealed that, except for some samples, the parameters were not significantly different from the standard values provided by the WHO and ISIRI. The quality of well water and tap water was compatible with the standards and there was no problem with them. The inconsistencies in the water quality of some wells with the standards were as follows:

Wells 9, 18 and 19 in terms of EC, wells 9, 17, 18, 19 and 20 on TDS, well 10 on chloride, well 19 on turbidity and wells 18 and 19 on hardness level showed inconsistencies with the standards. However, the differences were not significant.

The water quality inconsistencies in some of the samples collected throughout the city with the standards were as follows:

In terms of pH, sample 3 had inconsistency with the standards, and in terms of nitrate content, samples 3 and 6 had a higher nitrate content than other samples. In sample 3, the nitrate content was considerable, equal to 89 mg/L, which was higher than the standard value of 50 mg/L; but sample 6 showed a value of 39 mg/L that was not higher than the standard but had a higher nitrate content than other sampling sites.

Table 4 shows an analysis of microbial, physical and chemical parameters in bottled drinking water samples. Except for some cases, the mean of all parameters in all brands was lower than the permissible levels of WHO, ISIRI and IBWA.

In terms of the bottled water quality inconsistency with the IBWA standard, the observations were as follows:

In terms of turbidity, brand 1 with turbidity 8 showed much higher turbidity than the standard. In terms of nitrite, brands 1, 2, 5, 6, 7 and 10 were above the IBWA standard for nitrite.

As for nitrate, all the brands had some nitrate, while according to the IBWA standard for bottled water, this parameter must be zero. In terms of hardness, brands 1, 2, 4, 6 and 7 had hardness values above the IBWA standard. Differences in the quality of various brands of bottled drinking water can be attributed to the quality of water purifiers or geographical differences in water resources, precipitation, mineralogy of aquifer rocks and regional topography, which provide water for bottled water companies (Mohammadi et al., 2019).

In a study by Dindarloo in Bandar Abbas (Dindarloo et al., 2016), it was revealed that the quality of some parameters, such as pH, in some brands was not consistent with the standard. But in terms of other parameters, the physicochemical and microbial quality was similar to the results of the present study.

Naddeo conducted a comparison between the quality of bottled water and standards provided for bottled water in Italy (Naddeo et al., 2008). The results showed that several parameters were not consistent with these standards.

Using the statistical tests, the quality of parameters measured in three groups of drinking water suppliers in Shahroud (well water, tap water and bottled water) was compared. Supplementary Material 1 (SM1) and Table 5 show the results of one-way ANOVA and the SNK test, respectively. ANOVA explains the mean differences in the three groups and interprets the significance or non-significance of mean differences in three groups. The SNK test investigates the pairwise significance of the mean differences in groups.

According to the data of ANOVA analysis in SM1, except for EC, turbidity and hardness parameters, the mean of other parameters was significantly different in the three groups. Figure 2 shows the ANOVA analysis visually in which the comparison of the mean values of the parameters with the standard is shown.

Table 5 shows that the water quality of the two groups of bottled water and water available in urban water supply is not significantly different in terms of EC, turbidity, TDS, nitrite and hardness, which clearly shows a lack of need for bottled water, instead of tap water. A comparison of the quality of bottled water and well water demonstrated that, except for pH, TDS, chloride and nitrite, there was no significant difference between the quality of bottled water and well water.

An examination of Table 5, which compares the quality of well water and tap water, showed that, except for fluoride and nitrate, there was no significant difference between the quality of well water and tap water, which was obvious, because wells are the main water suppliers in the tap water system. The small difference between the quality of these two groups can be due to probable problems in the water distribution network or water storage tanks.

The results of the tables presented based on data analysis showed that the microbial quality was excellent in all three groups and no microbial problems were observed in any of the groups.

According to the WHO program for safety of water, the water safety plan (WSP) approach has been developed to organize and systematize a long history of management practices applied to drinking water and to ensure the applicability of these practices to the management of drinking water quality (WHO 2011).

Although Iran is one of the developing countries with WSP where the spread of waterborne diseases, especially cholera, has occurred in the past, it has now made significant progress in developing the microbial quality of water, as the results of the present study show (Gundry et al., 2004). This research is part of the WSP program implemented in Iran in the city of Shahroud. Like many WSP programs running in developing countries such as Nepal, Philippines and South-East Asia (WHO, 2016a, 2016b; Sutherland, 2017), this program in different cities of Iran is ongoing based on the instructions of WHO and has achieved significant success in water management.

In a study of the water resources of some developing countries, in different seasons, between 80 and 95% of water resources do not meet the physicochemical and bacteriological quality standards (Pritchard et al., 2016). However, in the present study, as can be seen in Tables 2–4, the microbial and physicochemical quality of all three water sources used in Shahroud is in accordance with national and international standards.

A study conducted two seasons before the rainy season and the rainy season on the physicochemical and microbial quality of drinking water in Pakistan's urban areas shows that, as in the present study, the pH does not contradict the standards, but in the case of turbidity in the rainy season, the turbidity was higher than the WHO limit.

In terms of fecal coliforms, 50% of the samples before the rainy season and 75% of the samples in the rainy season showed coliform pollution (Haydar et al., 2009).

Also, based on a broader study in Pakistan, which is one of Iran's neighbors, 33% of deaths were due to waterborne diseases (Daud et al., 2017; Chandio et al., 2019). However, in the present study, no bacteriological contamination was observed in any of the water resources of Shahroud.

In 2010, Ikem performed a study on the concentration of volatiles in bottles and tap water and showed that 97% of all types of tap water were safe and healthy for human use and that there was no need for bottled water (Ikem, 2010).

Cidu published a paper in which organic compounds were compared in bottled water and tap water in Italy. The results showed there were several compounds in many bottled water samples, which was inconsistent with Italian legislation on water and WHO guidelines (Cidu et al., 2011).

Regardless of the area in which this study was conducted, a question arises: Is it necessary to use bottled water when regional water quality is excellent? The results of the analysis of the parameters evaluated in this study indicated that the microbial, chemical and physical quality of well water and tap water was highly compatible with the national and international standards and did not pose a threat to consumer health. Therefore, there is no need for developing other types of water treatment systems such as bottled water and domestic water treatment systems. Since bottled water is exposed to intense sunlight during the transport process, in many cases, there could be a leakage of plastic monomers from the bottle wall into the water in hot or cold conditions (Bach et al., 2012; Mason et al., 2018; Filella, 2020), which can endanger consumer health. The quality of tap water in the water supply network of Shahroud was at an appropriate level, which did not threaten consumer health. However, many people resort to domestic water treatment, and any lack of attention in cleaning the filters in this treatment system could lead to a mixing of organic matter or microorganisms and their toxins into the water consumed, which many people are unaware of.

Bottled water imposes high costs on families because the price of bottled water is several times higher than that of other types of urban drinking water in the distribution network (Qian, 2018). The results of studies on urban drinking water quality show that there is no need for consuming bottled water. Increased public awareness on the quality of water available in the urban water network, the sensitivity of drinking water suppliers, and the environmental hazards of plastic pollution caused by bottled water can help decrease household costs and help the family economy (Doria, 2006; Saylor et al., 2011; Bach et al., 2012; Mason et al., 2018; Qian, 2018; Filella, 2020). However, providing a more accurate report on a comparison of the chemical and radiological quality of different water supply groups entails higher costs and requires more time.

M.G. and A.R. contributed to the writing and conceptualization of the research, S.N. and A.-B.J. contributed to the experimental works and the preparation of the methodology, and M.G. contributed in terms of software application and analysis of data.

This research was funded by Shahroud University of Medical Sciences, grant numbers 9769 and 9008.

The authors acknowledge the financial support (Grant # 9769 and 9008) provided by the vice chancellery of research and technology, Shahroud University of Medical Sciences, for this research.

The authors declare no conflict of interest.

All relevant data are included in the paper or its Supplementary Information.