Investigation of the chemical and microbial quality of water supplied by treatment stations in Kerman city, Iran Open Access

Water is considered one of the most important elements in human life and is a critical component in the human body, comprising 65–70% of the human body. It is also an essential factor in different vital processes (Nabizadeh et al. 2019). Humans have the necessary, continuous, and indispensable need for water. It must meet the quality standards in terms of physical, chemical, and microbial specifications to save human health (Yousefi et al. 2019). In recent decades, water pollution has increased. According to World Health Organization (WHO) reports, more than 80% of diseases in the world are directly or indirectly associated with polluted water (Alarbash 2023). Polluted drinking water can cause several diseases. Some evidence shows that exposure to pesticides by consumption of polluted drinking water may cause thyroid cancer (Norouzi et al. 2023). Exposure to microplastics through ingestion of polluted water can cause inflammation and damage internal cell layers due to the production of reactive oxygen species (Waghmare & Dar 2024).

Various research studies have been done to measure the quality of drinking water. A study, conducted on the quality of desalinated water in commercial stores in the municipality of Janzour, Libya, showed that the majority of samples meet the Libyan chemical and bacterial standards, except for calcium (Alarbash 2023). Investigating the drinking water quality and associated health risks in the metropolis area of Pakistan showed that alkalinity, electrical conductivity (EC), and arsenic were higher than WHO standards. Also, the water quality index of most samples was poor (Sohail et al. 2022). Pourakbar et al. reported that the majority of the physicochemical parameters of the drinking water in Ardabil, Iran were below the national drinking water standards and the use of household water purification devices was not recommended in this city (Pourakbar et al. 2022). The evaluation of drinking water quality and health risk assessment of heavy metals in rural areas of Kurdistan, Iran showed that, except for arsenic and nitrate, the values of other parameters were below the national drinking water standard levels (Maleki & Jari 2021). Water treatment in decentralized stations is one of the methods to supply treated drinking water in Iran, especially in cities with poor-quality water in distribution systems. Groundwater sources that pass processes of chlorination and storage are the primary source of drinking water in Kerman city, the capital of Kerman province located in the southeast of Iran. To the best of our knowledge, there has been no research on the water quality supplied by treatment stations in Kerman city. Consequently, the present study aimed to fill this gap of knowledge by investigating the chemical and microbial quality of water supplied by these stations and comparing it with the WHO and national standards of drinking water.

The methods of Ethylenediaminetetraacetic acid (EDTA), titrimetric for total hardness (TH), colorimetric for nitrite, ultraviolet spectrophotometric screening for nitrate, the electrode for total dissolved solids (TDS), EC, the most probable number for total coliforms (TCs) and fecal coliforms, and inductively coupled plasma equipped mass spectrometry detector (ICP-MS, Model: Arcos, Germany) for 13 elements were used according to the standard methods for the examination of water and wastewater in 2017 (APHA 2017).

The value of parameters in the samples was reported by mean ± standard deviation (SD). The mean values in different seasons and five SPW were compared by the ANOVA test. Statistical analysis was done by R software version 3.6.2, and the p-value less than 0.05 was considered as the significant level.

The mean concentration of chemical characteristics in four seasons had no significant difference except for nitrite (p-value < 0.001) and nitrate (p-value = 0.03). The minimum and maximum concentrations of nitrite were measured in summer and winter, respectively. The mean concentration of all chemical characteristics in five SPW had no significant difference.

In the present study, total and fecal coliforms were investigated in the water samples in four seasons, and results are shown in Table 1 as mean ± standard deviation. Total coliforms are not useful as an indicator of fecal contamination and have been proposed as a disinfection indicator (WHO 2022). Total coliforms include organisms that can survive and grow in water (Yousefi et al. 2018; Murei et al. 2024). The value of the TCs in our samples (5.30 ± 7.87) was higher than their values set in the national standard (0/100 mL). The mean difference between the seasons was significant (p-value = 0.04), but not between the stations (p-value = 0.47). Excursion of the value of TCs in the water samples in the study period could be associated with the absence of a disinfection process in the water treatment in the five SPW. The fecal coliform, Escherichia coli, was not detected in the samples collected from SPW, except in samples in autumn (2.00 ± 0.00). The mean difference of fecal coliform in different seasons (p-value = 0.27) and between SPW (p-value = 0.90) was insignificant. Due to the absence of disinfectant residues, the contamination of drinking water can be expected. E. coli occurs in high numbers in human and animal feces, sewage, and water subject to recent fecal pollution and is considered the most suitable indicator of fecal contamination. However, most strains of E. coli are harmless. However, specific strains, such as enterohaemorrhagic E. coli, can cause severe foodborne diseases (Yousefi et al. 2018).

In the current study, the suitability of drinking water supplied by the treatment stations in Kerman city was evaluated using water sampling in four seasons in 2022, analyzing chemical and microbial parameters and comparing them to the standards. As, Cd, Cu, Ni, and Pb were higher than the WHO and national standards. The concentration of TH, nitrite, nitrate, TDS, and EC in all seasons was not more than WHO and national standards. The TCs were detected in all samples in the values of more than the national standard. E. coli was detected in the samples collected in autumn.

The results of the present study showed that water treatment stations can reduce the concentration of some toxic elements, TH, nitrate, and nitrite in drinking water in the period of the study, while the concentration of some of them remained more than the standard. There is also a risk of removing useful elements. In terms of microbial factors, although fecal coliform of E. coli was not observed, TCs were observed due to a lack of disinfection. Therefore, according to the results, the use of these waters is generally not recommended. According to our findings, further studies on the water supplied by the treatment stations in Kerman city and other cities, continuous monitoring and supervision of the Ministry of Health on the performance of these units can be suggested.

This work was supported by the Vice Chancellor for Research and Technology of Kerman University of Medical Sciences under Grant Number 400001099 and the Code of Research Ethics certificate IR.KMU.REC.1400.676. The authors would like to acknowledge the Environmental Health Engineering Research Center of Kerman University of Medical Sciences.

M.F. and I.A. collected and designed the study. M.F., I.A., and T.D. collected the samples. M.F., T.D., and M.N.G. analyzed the samples. I.A. statistically analyzed the data. All authors contributed to writing and reviewing the manuscript.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.