1 Introduction

The issue of water is one of the most vital issues of human communities. Effective protection and use of water resources are among the principles of sustainable development in any country. The access to and use of healthy drinking water is essential to human life. The drinking water should be healthy, because if not so, it will cause various diseases and disorders. In addition, water plays a fundamental role in the environment and industries. Water pollution has been considered a serious threat to human beings and natural ecosystems in recent decades in a way that the investigation of the changes in water quality is one of the important factors in the effective use of water. Population growth, coupled with increasing water consumption, drastically reduces access to water for every individual and continues to put stress on biodiversity throughout the global ecosystem [1]. Access to healthy drinking water resources is an important issue in most countries in the world. According to WHO statistics, annually, 1.1 million people do not have access to healthy drinking water all over the world, and about 80% of children's deaths are due to digestive diseases such as diarrhea, etc. that occur after consuming contaminated drinking water [2]. In this regard, as has been reported in 2009, a child died every 20 s due to water-related diseases. Access to sufficient water resources is essential for human life. The main objective of the qualitative investigation of drinking water is to maintain the public health and well-being of the users. Drinking water with very high amounts of sulfate, chloride, or calcium carbonate leads to indigestion in most people. These minerals can cause severe diarrhea. The vast array of water-borne diseases and their significant impact on public health is a major concern with far-reaching consequences. Approximately 3.4 million people, the majority of whom are children, die each year from water-related diseases, with 2.2 million of these deaths attributed to diarrheal diseases [3]. Water contamination by pathogenic microorganisms poses a serious and growing threat to human health. Currently, various microorganisms are used as primary indicators for assessing water quality, with total coliforms and Escherichia coli (E. coli) being the most common. However, the increasing incidence of waterborne diseases from sources considered safe by standard microbial criteria raises the question of whether these microbial indicators are sufficiently reliable and sensitive to ensure water quality. At present, other microorganisms, including bacteria, enteric viruses, and protozoa, are being tested and used in different countries as alternative indicators for monitoring water quality [4]. Heavy metals are recognized as major environmental pollutants due to their toxicity, persistence, and bioaccumulation. Their sources include volcanic eruptions, rock weathering, and human activities such as mining, industrial processes, and agriculture. When these metals enter aquatic ecosystems, they cause environmental problems and negatively impact human health, while also accumulating in food chains [5]. Total Organic Carbon (TOC) serves as an important indicator for measuring the concentration of organic matter in water, playing a vital role in monitoring and controlling organic pollution within the aquatic environment. Rapid and long-term in-situ monitoring of TOC provides a foundation for early warning and effective control of marine pollution, significantly contributing to the study of the global carbon cycle. Comprehensive global systems—including ships, buoys, and monitoring stations—are employed to assess the marine environment [6]. Organic matter in water is typically measured by Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD), both critical indicators of water pollution levels. The BOD to COD ratio reveals the biodegradability of wastewater, with higher ratios indicating lower biodegradability. A BOD to COD ratio below 0.1 suggests a high presence of organic matter that is difficult to degrade and potentially toxic. Water is easily biodegradable when the ratio is at least 0.4, with optimal values above 0.5. Various chemicals have been employed to reduce organic matter concentrations in water, aiming to lower its environmental risk [7]. Parameters such as pH, EC, TDS, turbidity, residual free chloride, alkalinity, hardness, calcium, magnesium, iron, nitrate, nitrite, sulfate, fluoride, and phosphate are among the most important physical and chemical parameters of drinking water. The lack or excess of some of these elements can endanger human health [8, 9]. For example, high concentrations of nitrate in drinking water can cause Methemoglobinemia in infants, and produce carcinogenic compounds such as Nitrosamines [10, 11]. Protection of drinking water and prevention of its contamination with pathogenic contaminators during the use of the drinking water pipeline network are important issues in any community [12]

Afghanistan is among the countries with the highest mortalities due to water shortage and hygiene (above 15%). About 20% of children’s mortalities in Afghanistan are due to diarrhea the main cause of which is contaminated water. Only 27.5% of the people in Kabul, the capital city of Afghanistan, have access to the central piping network. The majority of people in this city use shallow wells as the water supply. In addition, there is no general disinfection system in Kabul which has led to contamination of the water. Ideal drinking water should be clear, odorless, tasteless, stable (should not cause corrosion or sedimentation), and free of pathogenic organisms and other harmful compounds [13]. Countries around the world are concerned about the effects of unsanitary drinking water because water-borne diseases are one of the leading causes of illness and death [14]. Preventing water pollution is an essential issue. We must take action to preserve and use every drop of water [15]. The physicochemical properties of water are among the important parameters playing an important role in the maintenance of the healthiness of water and the satisfaction of the consumers. To set the parameters, the water should be tested. To assess the water quality, several parameters need to be measured and evaluated in a specific period. Setting the physicochemical parameters of water helps ensure it is not contaminated.

Numerous studies have been conducted on the quality of the drinking water in various provinces. Kakar et al. [16] evaluated some physicochemical parameters of water in some regions and counties of Herat Province and showed that generally, the drinking water in the investigated regions is potable and has no serious problems [16]. Ebner et al. analyzed the water in Herat Province (235 samples collected from the pipeline system and private wells) and showed that the samples do not contain heavy metals contaminations. In addition, 43.9% of the samples contained detectable amounts of coliforms [17]. In a study by the DACAAR (Danish Committee for Aid to Afghan Refugees) Institution in 2009 on refugees, it was indicated that microbial and sewage contaminations were detected in 59% of the subsurface waters in the Kabul district [18]. A survey conducted in Kabul by the BGR and AGS during 2004–05 indicated that 50% of the normal wells in this city are contaminated [19].

Thus, based on the above-mentioned, and the necessity of continuous evaluation of the urban pipeline systems quality and the lack of sufficient, comprehensive, and new research in this field in Herat Province, the present study aimed to provide a clear image of the physicochemical quality of drinking water in Herat Province and compare it to the WHOs standards.

2 Methods and materials

2.1 Study area

Herat is located in the western part of Afghanistan. Together with Badghis, Farah, and Ghor provinces, it makes up the northwestern region of Afghanistan. Latitude and longitude coordinates are 34.343044, 62.199074. in Herat, precipitation is scarce and amounts to 240 mm per year. There is usually no rain during the hot months of June through September and relatively high rainfall between December and March [20].

2.2 Sample collection

Water samples were collected from 15 regions in Herat Province. In each region, sampling was done in three iterations for each parameter. A total of 45 samples were collected. Samples were collected utilizing sterilized polyethylene bottles, which were rinsed with the respective sampling water before collection. Following collection, the samples were promptly transported to the laboratory and stored at a temperature of 4 °C to mitigate any potential chemical alterations.

2.3 Analytical methods

Sensory evaluation techniques were utilized to assess the color, odor, and taste of water samples directly at the collection site. The analysis was conducted following the Flavor Profile Analysis (FPA) method by a panel of five trained assessors. Before evaluation, the water samples were stored in glass containers and allowed to reach room temperature (25 °C).

The color of the water was visually examined in clear, transparent containers by a panel of 5 semi-trained individuals, with any turbidity or color changes documented.

Odor intensity was measured using the Odor Threshold Test (OTT), which determines the concentration at which odor is perceptible. The results were recorded on a 7-point scale, ranging from “very weak” to “very strong,” and the Odor Number (TON) was used as the unit of measurement for quantifying odor intensity. This test was performed directly at the collection site for each sample to avoid any changes during transport, and the evaluation was conducted by a panel of 5 semi-trained individuals.

The taste of the water was evaluated according to standard criteria, with the intensity similarly recorded on a 7-point scale. The evaluation was conducted by a panel of 5 semi-trained individuals.

Temperature measurements were conducted on-site using a Beckman model C310 thermometer, with readings taken once the temperature had stabilized.

The pH levels of the water samples were assessed in situ using a Hanna pHep® meter. In this procedure, 100 ml of each sample was placed into a sterile beaker, and the pH meter electrode was immersed in the sample. The pH value was documented once the reading had stabilized.

Turbidity and total hardness were quantified using photometric techniques with the model 321 PSaw (India). Initially, the collected water samples were filtered to remove any particulate matter that could interfere with the measurements. For turbidity assessment, formaldehyde was used as the reagent. The filtered water samples were treated with a known concentration of formaldehyde, and turbidity was measured photometrically.

To determine the total hardness, the EDTA titration method was employed. This method allows for the precise quantification of calcium and magnesium ions in the water sample, which together define the total hardness. The procedure involved the preparation of a buffer solution to maintain a pH of 10, which is crucial for the titration process. Eriochrome Black T was then added to the sample, forming a red complex with the calcium and magnesium ions present.

A standard EDTA (ethylenediaminetetraacetic acid) solution was gradually titrated against the prepared water sample. The titration continued until a color change from red to blue was observed, indicating the endpoint of the reaction and signaling that all calcium and magnesium ions had reacted with the EDTA. This methodology provides a reliable measure of total hardness, allowing for an accurate assessment of the water quality in relation to its hardness.

Electrical conductivity measurements of the water samples were carried out on-site using a COND 3110 SET 1 2CA101 conductivity meter, manufactured in Germany. A 100 ml portion of each sample was transferred into a clean beaker for testing. Prior to each set of measurements, the conductivity meter was calibrated according to the manufacturer’s instructions. The electrode was then placed into the sample, and the conductivity reading was recorded once it had stabilized.

Fluoride, nitrate, calcium, and magnesium, were analyzed using a spectrophotometer (Shimadzu UV-1240 model). Zirconium-Alizarin Complexone was employed for fluoride measurement, N-(1-naphthyl)-ethylenediamine dihydrochloride for nitrate, O-CPC for calcium, and Calmagite for magnesium [21, 22].

Total dissolved solids (TDS) were determined through an evaporating dish method. One liter of each sample was stirred and filtered through filter paper, which was subsequently washed three times. The filtrate was then transferred to an evaporating dish and dried. After cooling, the dish was weighed to ascertain the TDS, calculated using the appropriate formula.

$${\text{TDS (mg/L)}} = \frac{{\left( {A - B} \right)x1000}}{Volume of Sample}$$
(1)

where A = weight of dried residue + dish (mg).

B = weight of dish (mg).

2.4 Water quality index (WQI)

Objectively assessing water quality presents significant challenges; however, a commonly employed approach is the Water Quality Index (WQI). In the present study, we utilized the Weighted Arithmetic WQI to evaluate water quality. The computation of the WQI entailed the following procedures:

2.4.1 Assigning weights to each parameter

Each water quality parameter was allocated a weight (\({W}_{i}\)) corresponding to its influence on drinking water quality. Parameters that exhibited more significant adverse effects were assigned higher weights [23]. The assigned weights for each parameter are listed in Table 1.

Table 1 Weights assigned to each parameter
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2.4.2 Calculating Relative Weight (\({W}_{i}\)) The relative weight (\({W}_{i}\)) for each parameter was calculated using Eq. (2).

$$W_{i} = \frac{{\omega_{i} }}{{\mathop \sum \nolimits_{i = 1}^{n} \omega_{i} }}$$
(2)

\({W}_{i}\) represents the relative weight (weighted factor), while \({\omega }_{i}\) refers to the assigned weight for each quality parameter, and \(n\) indicates the number of selected parameters.

2.4.3 Calculating Quality Rating (qi) Using Eq. (3), the sub-index for the water quality rating (qi) is determined as follows:

$$q_{i} = \frac{{C_{i} }}{{S_{i} }}100$$
(3)

Where qi is the quality rating, Ci represents the concentration of each parameter in every water sample, and \({S}_{i}\) refers to the value of each quality parameter as specified by the WHO.

2.4.2 Calculating Sub-index (\(S{I}_{i}\)) the sub-index for each parameter was calculated as follows:

$$SI_{i} = \sum W_{i} *q_{i}$$
(4)

where \(S{I}_{i}\) represents the sub-index of the \(i\) th parameter, \({q}_{i}\) is the quality rating of the \(i\) th parameter, and \({W}_{i}\) denotes the relative weight of the parameter.

2.4.3 Calculating Final WQI Ultimately, WQI was determined using the following calculation:

$$WQI = \sum SI_{i}$$
(5)

3 Results and discussion

The data obtained from the water quality analysis, including mean, minimum, and maximum values, are summarized in Table 2. These values are compared with WHO standards in Table 2 and illustrated in Figs. 1, 2, 3. The full details of the 45 water samples tested, including their specific parameters and corresponding results, are provided in the supplementary file (1). These data can be obtained from the corresponding author upon reasonable request.

Table 2 Summary of minimum, maximum, mean, standard deviation, and comparison of values to WHO standards
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Fig. 1
figure 1

Comparison of the mean measured parameters of water samples across Herat province with the standards of the WHO

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Fig. 2
figure 2

Comparison of the mean measured parameters water samples across Herat province with the standards of the WHO

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Fig. 3
figure 3

Comparison of the mean measured parameters of water samples across Herat province with the standards of the WHO

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The sensory qualities of drinking water, including its taste and odor, profoundly impact how consumers perceive and accept it. These aesthetic factors are critical in shaping user confidence and satisfaction with water quality [24].

Overall, the color, odor, and taste of the drinking water in this region are within acceptable limits (Table 2).

Most water samples were colorless; though slight turbidity was noted in a few cases.

A faint chlorine odor was detected in some samples, while the majority exhibited no noticeable odor.

The taste of the water was generally acceptable; however, a mild bitterness was observed in certain areas, likely due to increased mineral content.

Some contaminants in water can often be identified by assessing its color, odor, turbidity, and taste. For instance, the presence of reddish-brown particles may indicate the presence of iron, while black particles suggest the presence of manganese. These contaminants form when the oxygen in the plumbing system oxidizes these metals, leading to their precipitation [25]. However, most contaminants are not easily detectable and require testing to determine whether the water is contaminated. Consequently, contaminants can result in unpleasant tastes or odors, staining, and potential health effects [26].

The turbidity of the drinking water samples collected from Herat Province ranged from 0.6 to 1.02 NTU. The mean turbidity was 0.93 NTU (Table 2), which is above the Highest Desirable Limit (0.5) and under the maximum allowable limit (5). Turbidity is one of the indicators for determining water quality. Turbidity is caused by organic matter and inorganic particles suspended in water [27]. Turbidity is considered a standard indicator for assessing drinking water quality. It reflects the amount and physical characteristics of suspended particles, though it does not provide information on the type or source of these particles. Turbidity can be measured quickly, easily, and cheaply, serving as an effective early indicator of water quality changes. Particles contributing to turbidity can reduce the effectiveness of chlorine in inactivating microorganisms. Additionally, turbidity is often associated with increased runoff and the introduction of particles and microbial loads into the system, particularly following rainfall events [28].

The electrical conductivity of drinking water in Herat Province ranged from 1222 to 1680 µS/cm with a mean value of 1328 µS/cm (Table 2), which is above the Highest Desirable Limit (900) and under the maximum allowable limit (1400). Electrical conductivity is utilized to assess the overall ionized content of water, directly correlating with the combined levels of cations and anions. Given that the majority of salts in water exist in ionic form, they enable water to conduct electricity. Consequently, conductivity provides a reliable and prompt assessment of the total dissolved solids in water, thereby serving as an effective gauge of TDS, which plays a significant role in determining the salinity and palatability of potable water [29].

The flavor of water can be influenced by the presence of dissolved solids. Water quality is assessed by taste panels according to its Total Dissolved Solids (TDS) concentration, categorized as Excellent (less than 300 mg/L), Good (300 to 600 mg/L), Fair (600 to 900 mg/L), Poor (900 to 1200 mg/L), and Unacceptable (greater than 1200 mg/L) [30]. The overall mean TDS in the present study has been 576.8 in the 400–718 mg/L range (Table 2), which is above the Highest Desirable Limit and under the maximum allowable limit.

The pH of the samples ranged from 7 to 7.5, with a mean value of 7.32 (Table 2), which is in the natural and allowable range. The WHO recommends a pH range of 6.5 to 8.5 for safe drinking water [31]. Both the WHO and national guidelines, such as those from the U.S. Environmental Protection Agency (EPA), suggest this range as acceptable for drinking water [32]. The pH level influences bacterial growth and the presence of contaminants in water. Extremely high or low pH can make water unsuitable for certain uses. At high pH levels, metals tend to precipitate, and chemicals like ammonia become toxic, leading to unpleasant taste and odor in water. At low pH levels, metals are more soluble, and chemicals such as cyanide and sulfide become more toxic. Acidic water can also corrode metal pipes, making heavy metals more bioavailable and toxic. Exposure to extreme pH in water can irritate eyes, skin, and mucous membranes. Monitoring pH levels is a common method for detecting water pollution [33].

The concentration of fluoride in drinking water samples in Herat Province ranged from 0 to 0.3 mg/L, with a mean value of 0.2 mg/L (Table 2), which is under the amount needed for the body and indicates the fluoride shortage. The use of low-fluoride waters can lead to tooth decay. The fluoride amounts above the allowable limit in drinking water can also lead to dental fluorosis, while much higher amounts can also cause skeletal fluorosis [34, 35].

Nitrate ions significantly influence human health and the environment, with their overuse leading to detrimental effects on the ecological system and natural surroundings [36]. The amount of nitrate in water samples in Herat Province ranged from 1.4 to 25.835 mg/L with a mean value of 12.014 mg/L, which is within the suitable range.

Calcium and magnesium exist in all waters stemming from the rocks, however, compared to calcium, the magnesium amounts are usually lower, which can be due to lower amounts of magnesium in the earth’s crust [37]. The high amount of magnesium in water can cause an unpleasant taste [34]. The calcium and magnesium amounts in Herat water samples ranged from 5 to 10.4, and 0 to 15 mg/L, respectively, with overall mean values of 6.8 and 11.25 mg/L, which are within the suitable range.

The total hardness of the drinking water in Herat Province ranged from 54 to 67 with a mean value of 58.33 mg/L as CaCO₃, which is appropriate. Hard water is known to result in the formation of soap scum and necessitates a higher amount of soap for lathering. The level of water hardness is commonly quantified in milligrams of calcium carbonate equivalent per liter. Water is categorized as soft when its calcium carbonate concentration is below 60 mg/L, medium hardness between 60 and 120 mg/L, hard between 120 and 180 mg/L, and very hard when exceeding 180 mg/L. While cations are the primary cause of water hardness, they can also be classified as carbonate (temporary) and non-carbonate (permanent) hardness [38].

Water quality was classified as “poor” based on the Water Quality Index (WQI) calculation, which is a widely used tool for assessing water quality. The WQI was determined using parameters such as temperature, turbidity, electrical conductivity (EC), TDS, pH, fluoride, nitrate, calcium, magnesium, and total hardness. Each parameter was weighted according to its significance (Table 1). The final WQI for the water samples was 53.05, falling within the “poor” category (51–75) based on standard classifications (Table 4). The classification is supported by comparisons with WHO standards and the proximity of key parameters, such as EC and hardness, to their maximum allowable limits.

The results of the WQI calculations based on the collected data are shown in Table 3.

Table 3 summarizes the results of WQI calculations for the analyzed parameters, including mean values, WHO standards, relative weights, quality ratings, and sub-indexes for each parameter
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The final WQI value is:

WQI = 6.575 + 1.744 + 11.857 + 7.21 + 12.2 + 2.083 + 3.004 + 0.567 + 2.344 + 5.466 = 53.05.

Based on the calculated WQI value of 53.05, the water quality falls into the “Poor” category, as shown in Table 4.

Table 4 Classification of water quality based on WQI values with the corresponding ranges for different categories
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Physicochemical parameters are among the important properties for the determination of the drinking water quality, which should be taken into consideration to maintain the health and development in society. In this regard, some rules have to be established (e.g., regulatory limits for acceptable pH, turbidity, total dissolved solids, and allowable concentrations of contaminants such as heavy metals and pathogens, by national and international guidelines such as those set by the World Health Organization or local environmental agencies).

In addition to hygiene problems, physical, chemical, and microbial undesirable drinking water can lead to an unacceptable appearance and distrust among the consumers of the urban water distribution network, and make them use other water supplies, such as bottled water, private wells, or water from nearby rivers and streams.

This study primarily focused on the measurement of physicochemical parameters of water. While microbial quality, heavy metal contamination, and BOD and COD were not included in this analysis due to practical constraints, these factors are crucial in providing a more detailed understanding of water quality. It is suggested that future studies incorporate these aspects to complement the current findings and offer a more comprehensive assessment of water safety.

4 Conclusion

This study comprehensively evaluates the physicochemical parameters of drinking water in Herat Province. In some cases, parameters such as electrical conductivity (EC), turbidity, and total dissolved solids (TDS) either exceeded or approached the recommended limits set by the World Health Organization (WHO), indicating the presence of suspended particles and high ion concentrations. The Water Quality Index (WQI) classified the overall water quality as "poor" with a score of 53.05, primarily due to the proximity of EC and TDS values to the Maximum Allowable Limit (MAL).

Key parameters such as pH, nitrate, calcium, magnesium, and total hardness were within acceptable ranges, indicating the absence of common chemical contaminants. While the deficiency of fluoride poses potential dental health challenges, it does not constitute an immediate public health risk.

To improve water quality management, continuous monitoring of drinking water sources, particularly in areas where EC and TDS values are approaching critical thresholds, is essential. Additionally, public awareness programs regarding the importance of regular water testing, along with the adoption of effective filtration methods and improved water treatment infrastructure, can help mitigate these challenges. By implementing such measures, Herat Province can make significant strides toward enhancing water quality and aligning it with international health standards.

This study primarily focused on assessing the physicochemical parameters of drinking water. Due to practical limitations, microbial quality, heavy metal contamination, and the measurement of BOD and COD were not investigated. Including these factors in future research could provide a more comprehensive understanding of water safety. These critical areas present opportunities for further investigation to complement the current analysis.