Groundwater quality evaluation for drinking purpose using water quality index in Kathmandu Valley, Nepal

ABSTRACT Groundwater is a significant source of drinking water in Kathmandu Valley of Nepal. The study aims to evaluate the groundwater quality in terms of water quality index. We compared the physicochemical and microbial parameters of 159 groundwater samples. The study showed that conductivity, hardness, chloride, and nitrate were found to be significantly higher in well water and ammonia was found to have significantly higher concentrations in boring water. The Spearman’s rank correlation coefficient demonstrated a positive correlation between conductivity and hardness, turbidity and iron, total hardness and chloride, and ammonia and arsenic. The drinking water quality parameters including pH, conductivity, turbidity, chloride, hardness, iron, ammonia, total coliform, and Escherichia coli count exceeded National Drinking Water Quality Standards, 2022 by 7.55%, 22.01%, 50.94%, 1.26%, 3.77%, 69.81%, 41.51%, 93.71%, and 47.17% samples, respectively. The water quality index showed that 38.36% of groundwater samples fall under grade-E which requires proper treatment before use. Linear regression revealed that with the increase in turbidity and iron, the water quality index also increases. The principal component analysis identified hardness, iron, conductivity, and nitrate as the major variables governing groundwater quality with no significant difference between well and boring water. Results suggest an urgent need for appropriate treatment of groundwater to mitigate pollutants.


Introduction
Globally, 844 million people were still without access to a basic drinking water service in 2015 (WHO and UNICEF, 2017) and more than 2 billion people reside in nations with high water stress (WWAP, 2019).Growing water stress is a sign of intensive water resource usage, which has a negative impact on the sustainability of water supplies.An impending water crisis is imminent with rampant groundwater extraction, declining water table, and water quality (ADB, 2016).Water supply is directly impacted by poor water quality, which also raises health hazards associated with drinking water (WWAP, 2019).Numerous water-borne illnesses, including cholera and schistosomiasis, are still widespread in many impoverished countries (WWAP, 2019).The Sustainable Development Goal 6 aimed to provide everyone with equal access to clean, affordable drinking water by 2030.
Nepal has huge water insecurity as large people do not have adequate water to meet their demands due to competition among water users for scarce resources (Pandey, 2021).Nepal ranks fifth out of six South Asian nations in 2020 with a national water security score of 52.3 out of 100.Its score is decreasing from 53.2 in 2016 to 52.3 in 2020.Nepal has water-related disaster security of 12.4, environmental water security of 13.3, urban water security-11.2,economic water security-9.7,and rural household water security-6 out of 20 (Panella et al., 2020).There is water insecurity in all sectors and a big gap between water supply and demand with increasing urbanization and industrialization.
Kathmandu Valley has severe water shortage and water quality degradation due to fast population increase and urbanization.The Kathmandu Valley's water demand is 470 MLD, while the average production is 114 MLD with an average supply of just 91 MLD, according to Kathmandu Upatyaka Khanepani Limited's (KUKL) annual report 2020.In 2015, KUKL barely met 31% of the water demands during the wet season and only 19% of the dry season in its service areas (KUKL, 2015).There is a significant gap between supply and demand.Water availability per capita is lower than the government of Nepal's basic water supply demand, with only 38 liters per capita per day lpcd in the rainy season and 22 lpcd in the dry (Tamrakar & Manandhar, 2016).There will still be a water supply constraint in the Kathmandu Valley even after the Melamchi water delivery project is finished (Shrestha, Manandhar, & Shrestha, 2020).The existing water distribution technique may not completely cover the valley, causing unequal distribution and social conflict (Thapa, Ishidaira, Pandey, Bhandari, & Shakya, 2018).The usage of shallow and deep groundwater resources is expanding to address the supplydemand gap (Udmale, Ishidaira, Thapa, & Shakya, 2016).
Groundwater supplies 25% to 40% of the world's drinking water globally (ADB, 2016).Groundwater is a reliable and major water resource in Kathmandu Valley to relieve the increasing water supply pressure (Chinnasamy & Shrestha, 2019).KUKL uses groundwater resources to meet 50% of the water demand of the Kathmandu Valley (Shrestha, Neupane, Mohanasundaram, & Pandey, 2020).Now, groundwater resources have become a major source of Kathmandu Valley.Urban water insecurity is a major emerging issue and is exaggerated by water pollution and solid waste management (Nepal, Neupane, Belbase, Pandey, & Mukherji, 2021).Unsustainable groundwater exploitation reduces groundwater quality and causes groundwater levels to drop (Pandey, Shrestha, & Kazama, 2012).Since groundwater is now the primary supply of drinking water in the Kathmandu Valley, its quality is a serious concern.More than 50% of groundwater sources in Kathmandu Valley are affected by groundwater pollution (Shrestha, Semkuyu, & Pandey, 2016).Surface land use and infiltration from it have a greater potential to affect groundwater.It is contaminated by seepage from septic tanks and soakaways, industrial discharge (Koju, Sherpa, & Koju, 2022), and domestic effluents.Groundwater is contaminated with pathogens (Sthapit et al., 2020), pesticides, and industrial effluents.In the Valley, deep groundwater has significant concentrations of ammonia, iron, arsenic, and nitrate, while shallow groundwater contains E. coli and nitrate (Khatiwada, Takizawa, Tran, & Inoue, 2002).Anthropogenic contamination is indicated by rising NO 3 − , Cl − , and SO 4 2-concentrations in groundwater (Jiang, Wu, Groves, Yuan, & Kambesis, 2009).Groundwater quality is affected by groundwater extraction, population growth, land use change, and urbanization, so it is vital to regularly monitor groundwater quality.Thus, the aim of this study is to evaluate the quality of groundwater for drinking purposes using an index of water quality.

Study area
The study focused on groundwater sources in Kathmandu Valley.Kathmandu Valley is a rapidly urbanizing city located between 27° 36' and 27° 48' N, between 85° 12' and 85° 31' E in the central part of Nepal.It lies at an altitude of about 1,300 masl.It is composed of Kathmandu, Bhaktapur, and Lalitpur districts (Figure 1).Approximately 664 km 2 is covered by the Kathmandu Valley watershed and drained by Bagmati River systems.The estimated population of Nepal has reached 29,192,480 in 2021 with unplanned urbanization and pollution (Timsina, Shrestha, Poudel, & Upadhyaya, 2020).
The study region has a climate that is warm, semitropical, and temperate, with an average annual temperature of 19.5°C and roughly 1089 mm of annual precipitation in 2017.The aquifer basin is divided into a shallow system and a deep system.There are three groundwater districts, including the northern, central, and southern groundwater districts, established within the basin.Micaceous quartz, sand, and gravel make up the unconsolidated permeable elements that make up the northern groundwater district.The central groundwater district contains the main urban area that is dominated by a thick layer of black clay.Basal gravel with a poor permeability layer and a thick clay layer make up the southern groundwater district (Dixit & Upadhya, 2005).

Sample collection
Altogether, 159 groundwater samples, 116 wells, and 43 borings were collected from Kathmandu Valley randomly.From the Lalitpur districts, 113 samples (94 wells and 19 borings) were collected.Similarly, 17 samples (8 wells and 9 borings) were collected from the Bhaktapur districts.From Kathmandu, 29 samples (14 wells and 15 borings) were collected for analysis.These samples were collected from the urban areas of the Valley.

Sample analyses
All analyses of groundwater samples were done at the Environment Research Laboratory of Nepal Academy of Science and Technology.The study measured four physical parameters (temperature, pH, conductivity, and turbidity), six chemical parameters (total hardness, chloride, ammonia, nitrate, arsenic, and iron), and two microbial parameters (total coliform and E. coli count).As soon as the water samples arrived at the lab, they were tested.When an immediate analysis was not possible, the samples were kept at 4 °C for preservation.18.2 MΩ (Millipore, Milli-Q) water was used to prepare all reagent solutions.The standard method for the testing of water and wastewater was used to analyze the water samples (APHA, 2017).All calibrated instruments and analytical-grade chemicals were used for the analysis.

Data analyses
Data analysis was carried out on R version 1.1.463.To determine whether the data were normal, the Shapiro test was used for each dataset.All physicochemical and microbial data were non-normal so non-parametric tests were applied.Mann-Whitney non-parametric test was done to observe the differences in physicochemical and microbial quality between well and boring water.The relationship between variables was determined using Spearman's rank correlation coefficient.All variables were evaluated for their percentage of exceeding the National Drinking Water Quality Standards (NDWQS, 2022).
The water quality index (WQI) was calculated to calculate the quality of each individual sample (Brown, Mccleiland, Deiniger, & O'Connor, 1972).WQI is a mathematical tool that reduces vast amounts of data to one single integer.It indicates the degree of water quality while eradicating expert water quality specialists' biases and subjective evaluations of the water quality.There are numerous water quality indices; the weighted arithmetic index method was used among them.The most frequently measured water quality variables were used in the weighted arithmetic water quality index method to classify the water quality according to its purity (Tyagi, Sharma, Singh, & Dobhal, 2013).
It is calculated as follows: The quality rating scale (Qi) as: where, the estimated concentration of ith parameter in the analyzed water is V i , the ideal value of this parameter in pure water is Vo, Si is recommended standard value of ith parameter The unit weight (Wi) for each water quality parameter is calculated by using the following formula: K is the proportionality constant, and the following equation can be used to compute it: Then, the water quality was then graded as excellent, good, poor, very poor, and unsuitable water quality (Table 1).
In multivariate analysis, principal component analysis was done.All the physicochemical and microbial data were z-standardized prior to analysis to remove variability in the data.Then, environmental variables were subjected to a multi-collinearity test, and variables with high collinearity were eliminated (Spearman's rank correlation matrix, r > 0.70).Among the 12 variables, 8 variables were selected for principal component analysis.

Groundwater degradation
The increasing population density, urbanization, and industrialization are driving forces to exceed groundwater extraction over recharge, decrease in water level and degradation of groundwater quality (Pandey, Chapagain, & Kazama, 2010).Effluents and sewages from residents, institutions, and industries are degrading the quality of groundwater.The Kathmandu Valley has the highest proportion of urban residents (about 50%) (ADB, 2019).In the past three decades, the urban area has increased by 412%, with the majority of this growth coming from the conversion of 31% agricultural land (Ishtiaque et al., 2017).The built-up area in Kathmandu Valley is increasing (Figure 2).The Kathmandu Valley had an urban density of 3738 people per sq km, which is around 6.5 times higher than the national average (CBS, 2016).Around 200 industrial units are housed in three industrial estates in the Kathmandu Valley: Balaju, Patan, and Bhaktapur.The combined wastewater production in these estates is estimated to be 800 m 3 /day (Shukla, Timilsina, & Jha, 2012).Wastewater generation in Kathmandu Valley urban region in 2001 was estimated to be 50.8 million liters per day (MoUD, 2015).The groundwater system is easily contaminated by nitrates and ammonia from human waste and agricultural operations; the groundwater close to the surface is particularly susceptible (Shakya, Nakamura, Kamei, Shrestha, & Nishida, 2019).
Kathmandu Metropolitan City's imperviousness increased from 18.71% in 1990 to 73.67% in 2010 ( UN-Habitat, 2015).As of 2010, 2020, and 2030, the volume of water recharge was anticipated to be 67.73,59.05, and 51.5 million cubic meters per year (MCM/ year), respectively.This clearly demonstrated a decrease in groundwater recharge in relation to a decline in the permeable regions (Shrestha, Shakya, Shrestha, & Khadka, 2023).Future reductions in  groundwater levels are anticipated further (Shrestha, Neupane, Mohanasundaram, & Pandey, 2020).The groundwater level is decreasing spatially and temporally in Kathmandu Valley (Figure 3).Uncontrolled development in Kathmandu and other urban centers is causing an increased frequency of urban infrastructure flooding.The Kathmandu Valley's communities were found to be most vulnerable to flooding and inundation.Almost every monsoon, especially in the places close to the rivers, the high intensity and prolonged precipitation results in frequent floods.In July 2002, there were 26 floods in the Kathmandu Valley, which resulted in 28 fatalities as a result of heavy flooding (UN-Habitat, 2015).

Physicochemical and microbial characteristics of groundwater
The pH of well water ranges from 6.15 to 8.35 whereas of boring water from 5.0 to 8.78.There was no significant difference between the pH of the well and boring water (w = 2527.5,p > 0.05, Mann-Whitney test).The conductivity of well water ranges from 92 to 1375 µS/cm and of boring from 12 to 926 µS/cm.Conductivity (w = 134.5,p < 0.05, Mann-Whitney test), total hardness (w = 3668, p < 0.001), chloride (w = 3684.5,p > 0.001), and nitrate (w = 3454.5,p > 0.001) were found to be significantly higher in well water, whereas ammonia (w = 1984, p < 0.01) was found to be significantly higher in boring water.However, other variables such as turbidity, iron, arsenic, total coliform, and E. coli count were not found to be significantly different between well and boring water as shown in Table 2.The Spearman's rank correlation coefficient (Figure 4) showed electrical conductivity of groundwater was positively correlated with total hardness (r = 0.65), chloride (r = 0.40), ammonia (r = 0.2), and nitrate (r = 0.26) and negatively correlated with temperature (r = −0.37).Turbidity was positively correlated with iron (r = 0.82), arsenic (r = 0.39), and ammonia (r = 0.48) while negatively correlated with pH (r = −0.30)and nitrate (r = −0.33).Total hardness was found to be positively correlated with chloride (r = 0.52), ammonia (r = 0.2), and nitrate (r = 0.30).Iron was found to be positively correlated with ammonia (r = 0.45) and arsenic (r = 0.33) and negatively correlated with pH (r = −0.30)and nitrate (r = −0.36).Nitrate was found to be positively correlated with chloride (r = 0.39) and total coliform (r = 0.25) and negatively with arsenic (r = −0.26).Ammonia and arsenic (r = 0.50) were found to be positively correlated with each other.

Evaluation of water quality variables with National Drinking Water Quality Standard (NDWQS), 2022
Out of the 11 parameters, arsenic and nitrate of groundwater were within the acceptable limit of NDWQS (2022).The physical parameters such as pH, conductivity, and turbidity of 7.55%, 22.01%, and 50.94%, respectively, of groundwater exceeded NDWQS (2022) as demonstrated in Figure 5.The chemical parameters such as chloride, total hardness, iron, and ammonia of 1.26%, 3.77%, 69.81%, and 41.51%, respectively, of groundwater exceeded NDWQS (2022).The total coliform count of 93.71% and E. coli of 47.17% of groundwater samples exceeded NDWQS (2022).
In comparing well and boring water, maximum water samples of both exceeded the standard of total coliform and E. coli.Chloride of 1.72% of well water exceeded standard but boring water did not exceed the standard.The pH of 16.28% in boring water exceeded the standard whereas only 4.31% of well water.The ammonia of 38.79% of well water exceeded the standard and 48.84% of boring water.

Water quality index
The water quality index was calculated based on nine physicochemical parameters: pH, electrical conductivity, turbidity, total hardness, chloride, iron, arsenic, ammonia, and nitrate.Groundwater quality index map of Kathmandu Valley is exhibited in Figure 6.The WQI index of groundwater of Kathmandu Valley ranges from 5 to 581.Out of 159 groundwater samples, 61 (38.36%) samples were categorized as grade E indicating unsuitability for drinking purposes.However, 42 samples (26.42%) fall under grade A which is excellent water quality, indicating that these water sources are safe for drinking, irrigation, and industrial purposes based on nine parameters.Similarly, 39 samples (24.53%) were under grade B, which is good water quality.This water can be utilized for domestic, agricultural, and commercial needs.Eleven samples (6.92%) were under grade C, which is of poor water quality and can only be used for irrigation and industrial use.Six samples fall (3.77%)under grade D, which is of very poor water quality.

Relationship of water quality index with physicochemical parameters
Linear regression between turbidity (explanatory variable) and water quality index (response variable) showed that with the increase in turbidity, water quality index increases (Y = 0.53X + 69.59, R 2 = 0.35, p < 0.001) (Figure 7a).Similarly, the linear regression between WQI and iron also showed that the increase in iron content in water increases water quality index (Y = 58.58X+ 6.01, R 2 = 0.78, p < 0.001) (Figure 7b).

Multivariate analysis
Identification of major Variables: Environmental factors were subjected to the multicollinearity test, and high collinear variables were eliminated (Spearman's rank correlation matrix, r > 0.70).Finally, among 12 variables, 8 (pH, electrical conductivity, total hardness, chloride, iron, ammonia, nitrate, and total coliform count) were selected for the principal component analysis.
Principal component analysis was done to identify the influencing variables governing groundwater quality.The first two axes explained 72% of the cumulative variance with the eigenvalue of axis 1 (λ 1 ) = 2.06 and axis 2 (λ 2 ) = 1.65.Principal component 1 is composed of conductivity, total hardness, chloride, and nitrate, and they are major influencing variables of it.Principal component 2 is composed of iron, ammonia, and nitrate, and they are the influencing major variables of it (Table 3).
Among the eight variables, iron, ammonia, nitrate, total hardness, conductivity, and chloride were found to be important variables governing   groundwater quality.Total hardness, iron, EC, and nitrate were found as major variables determining the groundwater quality.Iron showed a negative relationship with nitrate and total coliform.Similarly, ammonia and pH were found to be negatively correlated with each other.The ordihull plot showed that boring and well water was not significantly different from each other (Figure 8).

Discussion
This study assessed the groundwater quality which is degrading with the haphazardly increasing urbanization of Kathmandu Valley.Groundwater is severely contaminated with anthropogenic contaminants.Being a key source of drinking water for the Kathmandu Valley, the quality of groundwater is a crucial problem.

Physicochemical and microbial characteristics of groundwater
Parameters such as electrical conductivity, turbidity, arsenic, ammonia, nitrate, and E. coli of groundwater were found to be highly variable which may be due to the differences in soil type, geology, and pollution loads at different sites.The highest percentage of the total coliform count of groundwater samples exceeded NDWQS (2022) in groundwater water which indicates high fecal contamination in groundwater (Gaihre et al., 2022).Followed by iron content which exceeded the highest, it is contributed by sewage, acid mine drainage, industrial wastewater, weathering of iron-bearing rocks and minerals, and landfill leachate.Higher Fe concentrations in groundwater may have resulted via the interaction of organic materials and underground oxidized iron minerals, as well as from the dissolving of Fe 2 CO 3 found in rocks at low pH (Mondal, Singh, Puranik, & Singh, 2010).Conductivity, total hardness, chloride, and nitrate were found to be higher in well water.Higher conductivity in well water indicates the presence of dissolved solids and inorganics including chlorides, sulfides, and carbonate compounds in a higher amount than in boring water which is similar to the finding of (Ghartimagar, Khatri, Neupane, Joshi, & Joshi, 2020).A number of dissolved polyvalent metallic ions, primarily calcium and magnesium cations, contribute to the total hardness of water (WHO, 2010).Hardness in water is contributed due to rock-water interaction and human activities (Mande, Liu, Tchakala, & Chen, 2018).Groundwater often has a significant level of hardness (Oko, Aremu, Odoh, Yebpella, & Shenge, 2014;WHO, 2010) which is similar in our study.Hard water can result in scale buildup in heated water applications as well as in the water distribution system, generating insoluble metal carbonates (WHO, 2010).Chloride ions are highly mobile and produced by run-off containing inorganic fertilizers, landfill leachates, septic tank effluents, animal feeds, industrial effluents, and irrigation drainage.When chloride levels are higher than 250 mg/L, water can develop a discernible taste.Chloride increases the electrical conductivity of water and hence the corrosivity.The levels of metals in drinking water rise as a result of chloride's reaction with metal ions to create soluble salts (WHO, 2003a).Chloride concentrations in groundwater are higher in urban than in forestland uses, indicating human influence from sewage and animal waste (Mullaney, Lorenz, & Arntson, 2009).Nitrate is a common groundwater problem; conversion of nitrate to nitrite is toxic to health.Its concentrations over 3.0 mg/L are indicative of human activity (EPA, 2013).Fertilizer use and septic leakage run through runoff, soaking, and migrating to groundwater cause nitrate pollution (Feng, Wang, Lei, Wang, & Zhang, 2020).It causes tissue hypoxia and even death; nitrite forms N-nitroso carcinogens interacting with secondary or N-alkyl-amides.Blue baby syndrome or methemoglobinemia can occur in infants exposed to nitrate at levels higher than 10 mg/L (Fossen Johnson, 2019;Mensinga, Speijers, & Meulenbelt, 2003).A high concentration of these physicochemical parameters in well water indicates that boring water possesses better quality than well water which is similar to the finding of Oko, Aremu, Odoh, Yebpella, and Shenge (2014).This may be due to the shallow depth of wells rather than boring which is more susceptible to contamination from surface land use patterns.
Ammonia was found to be significantly higher in boring water than in well water.It is commonly found due to organic waste disposal, leaching from fertilizers, and sewage systems.Because of the aerobic conditions that allow microorganisms to use oxygen to break down organic carbon, nitrates are typically present in high concentrations in the top meter of groundwater.Nitrates are denitrified below this depth due to a persistent anaerobic environment where oxygen is scarce.Ammonia is therefore the main nitrogen species in deep aquifers because nitrification of ammonia cannot take place in the absence of oxygen.As a result, high ammonia concentrations are found at higher depths, while high nitrate concentrations are found close to the aquifer surface (Bittner, 2000).
The electrical conductivity of groundwater was found to be positively correlated with total hardness, chloride, ammonia, and nitrate.An indicator of the existence of dissolved inorganic substances including sodium, magnesium, calcium, iron, nitrate, sulfate, and phosphate is electrical conductivity.This is negatively correlated with temperature which was found in contrast to other studies such as in Barron and Ashton (2007) and Hayashi (2004).This may be due to the fact that groundwater samples were from different locations with varying periods of sampling.Turbidity was found to be positively correlated with the iron content of the groundwater which is similar to the study by Ghartimagar, Khatri, Neupane, Joshi, and Joshi (2020).It is the cloudiness that results from suspended particles in water (WHO, 2017).
The oxidized ferric form of iron (Fe 3+ ) is insoluble in water and forms a brown-red precipitate which increases the turbidity of water.Turbidity and arsenic were also found to be moderately correlated with each other which is in line with the study by Gwachha, Acharya, Dhakal, Shrestha, and Joshi (2020).Similar to the study by Shrestha, Semkuyu, and Pandey (2016), iron was negatively correlated with pH as there is the dissolution of metals in acidic media.Several forms of iron in water are pH dependent.Fe 2+ is the most common type of dissolved iron in the pH range of 5.0 to 8.0, whereas iron bacteria are present in the pH range of 5.5 to 8.2.The soluble Fe 2+ is converted to insoluble Fe 3+ with increasing pH (Ibrahim, 2016).The correlation between As and Fe may point to a decoupling between the mobilization of As and Fe 2+ (Diwakar, Johnston, Burton, & Shrestha, 2015).Arsenic would be desorbed and iron would be released in an anaerobic environment as a result of the reduction of arsenic and Fe oxyhydroxides(II) (Smedley & Kinniburgh, 2013).Ammonia and arsenic were found to be positively correlated with each other.High NH 4 -N levels in groundwater operate as a nutrient for microbial activity, which reduces groundwater conditions and encourages arsenic release (Kurosawa, Egashira, & Tani, 2013).Ammonia is a good indicator of microbial activity in anoxic groundwater.Arsenic, ammonia, and iron enable the reductive dissolution of FeOOH (Dowling, Poreda, Basu, Peters, & Aggarwal, 2002).

Water quality index
The water quality index is a reliable method for understanding the overall quality of the water.Maximum analyzed groundwater samples were not suitable for drinking and need proper treatment before any usage which is the same as found by Gaihre et al. (2022); Maharjan, Joshi, Koju, and Shrestha (2020) and Koju, Prasai, Shrestha, and Raut (2014).The study found 26.42% were under excellent water quality based on nine physicochemical parameters, which are safe for drinking, irrigation, and domestic use.Linear regression showed an increase in turbidity, and iron in groundwater increases the water quality index.The increasing water quality index is shifting toward poor water quality.Turbidity is the suspended particles, chemical precipitates, and organic particles which decreases their clarity and quality.Insoluble iron (III) hydroxide, which precipitates from iron(II) salts and settles as rust-colored silt.Iron(II) concentrations in the anaerobic groundwater may reach several milligrams per liter without causing any coloring or turbidity in the water (WHO, 2003b).An increase in both parameters decreases water quality.

Multivariate analysis
Principal component analysis showed that total hardness, iron, electrical conductivity, and nitrate were major variables determining groundwater quality.Total hardness and iron loading factors were found to be high, indicating a natural origin in groundwater.The pH with negative loading factors may depict that the mobilization of iron is suitable in low pH and reducing environment which releases iron oxyhydroxide precipitation (Schürch, Edmunds, & Buckley, 2004).Fertilizer use and septic leakage run through runoff, soaking, and migrating to groundwater cause nitrate pollution (Feng, Wang, Lei, Wang, & Zhang, 2020).

Conclusion
The study showed iron and hardness were the most influencing factors governing the groundwater quality of Kathmandu Valley.Total coliform count, iron, and turbidity were found as the main problems in the groundwater of Kathmandu Valley.In conclusion, most of the groundwater falls under unsuitable water quality and was not within the permissible limit of (NDWQS, 2022).Using the groundwater of Kathmandu Valley without any treatment can cause various water-borne diseases.As a result, groundwater must be regularly monitored and properly treated before usage.If groundwater is properly treated and regularly monitored, it is the best alternative to reduce water insecurity in Kathmandu Valley.

Figure 1 .
Figure 1.Study area (a.Nepal map with Kathmandu, Lalitpur, and Bhaktapur districts, b.Kathmandu Valley with watershed, elevation, and sampling points).

Figure 2 .
Figure 2. a) Geomorphic map, b) geologic map, c) soil map, and d) land use map with built-up areas, major industrial sites, and drainage as a source of pollution to the groundwater of the Kathmandu Valley.(Source: (ISRIC, 2009)).

Figure 6 .
Figure 6.Ground water quality index map of Kathmandu Valley.

Figure 7 .
Figure 7. Linear regression between water quality index and (a) turbidity and (b) iron of water at 1 and 157 DF (n = 159).

Table 2 .
Physicochemical characteristics of groundwater of Kathmandu Valley.

Table 3 .
Factor loadings and eigenvalues of the principal components 1 and 2.