Appraisal of groundwater quality and its suitability for drinking purposes: the case of Damot Gale Woreda, Wolaita Zone, Ethiopia Open Access

Since water is the lifeblood of the world, it is considered an essential national resource. The availability of water resources was linked to both economic and social progress, suggesting that development was significantly impacted by the availability and management of these resources. This natural resource is found either on the surface (Beza et al. 2023) or on the ground (Winter et al. 2005).

In many nations, groundwater is the primary supply of water for industrial, agricultural, and residential uses. Presently, groundwater abstraction accounts for 26% of all freshwater removal worldwide, providing nearly half of all drinking water and 43% of irrigation consumption (Taylor et al. 2013; Koncagül & Tran 2022; Mseli et al. 2023). The only dependable supply of water in dry and semi-arid areas is groundwater (Mseli et al. 2023). Most people agree that groundwater is far cleaner than surface water. However, several variables impact the quality of groundwater, including the release of domestic, agricultural, and industrial wastewater, land use practices, geological formations, rainfall patterns, and infiltration rates (Stefanakis et al. 2015; Xiao et al. 2023).

Water naturally contains a wide variety of dissolved inorganic elements. These comprise calcium, magnesium, sodium, and potassium (cations) and chloride, sulfate, carbonate, and bicarbonate (anions), and they make up about 90% of the total dissolved solids (TDS) in water (Kahsay et al. 2019). Iron and strontium (cations) and nitrate, phosphate, and fluoride (anions) are examples of minor ingredients (WHO 2017). The content of trace elements such as As, Cr, Pb, Mn, and U will be less than 0.1 mg/L (Smedley & Kinniburgh 2002; WHO 2017).

The water's quality is determined by its physical and chemical properties, as well as any alterations brought about by human activities (Zeabraha et al. 2020; Chinthala et al. 2023). Water chemistry analysis is used to describe the physical, chemical, and biological characteristics of water concerning its suitability for a certain application.

To confirm if the observed water quality is appropriate for an intended application, the primary goal of the hydrochemistry evaluation is to comprehend the processes that determine groundwater quality, both naturally occurring and due to human activity, to fulfill the minimum requirement for drinking (Postma & Appelo 1936; WHO 2012). Although groundwater is an invisible resource that most people are unaware of, human activity and climatic variability put increasing strain on it, necessitating a global evaluation of groundwater quality (Giao et al. 2023). The groundwater quality index (GWQI) technique is used for assessing changes in groundwater quality across time and space (Pappaka et al. 2024). The process is predicated on the selection of several chemical parameters and the assumption of a weight based on the significance of each parameter. This weight is primarily inferred from the background and experience of the researcher. To assess the suitability of water for drinking, several researchers conducted GWQI (Giao et al. 2023; Tesema et al. 2023; Pappaka et al. 2024).

Enormous evaluations have been done on the appraisal of groundwater quality for drinking in Ethiopia (Kahsay et al. 2019; Zeabraha et al. 2020; Aragaw & Gnanachandrasamy 2021; Tegegne et al. 2023; Tesema et al. 2023). But unfortunately, so far, little has been done in the Wolaita Zone, particularly in Damot Gale Woreda. To address this gap, this study aims to evaluate the groundwater quality status, focusing on its suitability for drinking purposes. To address this problem, a research question was raised: how do seasonal variations and spatial distribution patterns influence the groundwater quality in Damot Gale Woreda, and is the water suitable for drinking purposes based on physicochemical parameters and the water quality index (WQI)? The novelty of this study lies in its comprehensive assessment of groundwater quality in Damot Gale Woreda, an area with limited prior research on this topic. By integrating seasonal variation analysis using analysis of variance (ANOVA) and spatial distribution mapping through Kriging in ArcGIS 10.3, the study provides valuable insights into both temporal and spatial groundwater quality dynamics. It not only evaluates multiple physicochemical parameters but also employs the WQI to categorize drinking water suitability in both dry and wet seasons. This integrated approach offers a robust methodology for groundwater monitoring and decision-making, serving as a baseline for future studies and sustainable water resource management in the region. The main limitation of the study was measurement error when the sample was taken.

The average elevation of the surrounding area, together with the precipitation and temperature records, places Damot Gale Woreda on the border between the temperate and tropical climate zones. The maximum temperature record is 27.2 °C, and the minimum temperature is 7.5 °C. Precipitation in the catchment has strong seasonal and elevation variability. The wet season extends from April to October. However, July and August are the wettest months of this season. The average annual rainfall is nearly 1,212 mm.

Data processing, quality testing, data organization, and geographic information system (GIS) input preparation were carried out after the required data was acquired. Following this, a two-season variation diagram was created using ANOVA, spatial data mapping was completed, and groundwater resource quality and drinking suitability were evaluated.

The selection of parameters to be analyzed depends on the purpose of the groundwater quality survey and monitoring goals, and this needs careful consideration.

The selection of water quality parameters in this study is justified based on their significance in assessing the potability, safety, and overall quality of groundwater for human consumption.

Physicochemical parameters (temperature, pH, TDS, electrical conductivity (EC)):

• Temperature influences chemical reactions, microbial activity, and the solubility of minerals.

• pH determines the acidity or alkalinity of water, affecting corrosion, solubility of metals, and biological processes.

• TDS and EC indicate the concentration of dissolved salts, minerals, and ions, affecting water palatability and usability.

Major cations and anions (Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, ⁠, ⁠):

• Calcium (Ca²⁺) and magnesium (Mg²⁺) are essential for water hardness, influencing scaling and human health.

• Sodium (Na⁺) and potassium (K⁺) affect drinking water taste and can pose health risks at high concentrations.

• Chloride (Cl⁻) in excess can indicate contamination and lead to a salty taste.

• Bicarbonate plays a role in buffering capacity and pH stability.

• Sulfate is essential to assess due to its potential laxative effects in high concentrations.

Nutrients and contaminants (⁠⁠, Fe, F⁻):

• Nitrate is a key indicator of agricultural and wastewater contamination, posing health risks such as methemoglobinemia.

• Iron (Fe) can cause discoloration, staining, and taste issues in drinking water.

• Fluoride (F⁻) is monitored due to its dual impact – beneficial at optimal levels for dental health but harmful at excessive concentrations, leading to fluorosis.

Turbidity: Turbidity measures water clarity and can indicate the presence of suspended particles, microbial contamination, and sedimentation issues.

To estimate the physicochemical properties of groundwater boreholes (BHs) and shallow wells (SHWs) to evaluate the quality of groundwater for drinking purposes, a total of 15 groundwater samples were collected from July to August of 2023 for the wet season and February 2024 for the dry season.

These samples were analyzed for sodium (Na⁺), magnesium (Mg²⁺), calcium (Ca²⁺), potassium (K⁺), chloride (Cl⁻), sulfate ⁠, carbonate ⁠, bicarbonate ⁠, nitrate ⁠, and fluoride (F⁻) within 48 h of collection. The water samples from 15 different sampling sites have been analyzed independently without combining the samples to assess the spatial variations in water quality across the BH. Samples should be collected from a well-mixed section of the BH after operation for 15–20 min. Samples were taken from each point by holding the collection bottle and lowering it into the water for the 20-min operation. Data collection was conducted with a prepared checklist. Before transporting to the locations, relevant materials and equipment for sample collection and analysis were prepared. The required materials and equipment include sample bottles, labels and marking pens, recording sheet, sample storage, transit containers, and on-site analysis testing apparatus. Samples for physical and chemical analysis were collected with a pre-cleaned (distilled) 1-L capacity bottle, while standard 1,000 mL glass bottles were used.

pH, temperature, TDS, and EC were measured in the field by using a pH/TDS/EC meter (Hanna HI 9811-5). To plot spatial distribution maps of various chemical constituents, ArcGIS software with Kriging interpolation was applied, and the ANOVA technique was used to show seasonal variations. A Kriging interpolation method helps to calculate a value for any unknown location and gives more weight to points closest to the prediction locations in the study area.

ANOVA is a very helpful approach in economics, biology, education, psychology, sociology, engineering, and business/industry research, as well as studies in many other domains. The ANOVA technique enables us to perform this simultaneous test and, as such, is considered to be an important tool of analysis in the hands of a researcher. The ANOVA was specifically used to test if there were any significant differences between samples among the sites and the seasons in the study area. Any chosen correlation between specific parameters was computed using Microsoft Excel to find the relationship between them. The groundwater sampled during the summer season of 2023 and the dry season in February from 15 selected wells distributed across the province was evaluated. The data domain selection was in line with the approach adopted by previous researchers (Kahsay et al. 2019; Giao et al. 2023; Tegegne et al. 2023; Kumar et al. 2024). The well parameters (e.g., well locations, depths, drilling diameter, and drilling purpose) are collected from the Southern Ethiopia Region Water and Irrigation Department Bureau. Spatial variation of the study area's groundwater quality was carried out using spatial analysis via ArcGIS 10.3. The Minister of Water Resources in Ethiopia undertook the laboratory testing of the chemical and microbiological properties. The collection, preservation, and chemical analysis were conducted following the American Public Health Association guidelines (APHA 2012).

In the laboratory, each parameter was examined during the study to assess the quality status and the potential pollution sources of the Damot Gale Woreda from July to August 2023 for the wet season and February 2024 for the dry season. The datasets were collected in both the rainy and sunny seasons.

The sampling points within the BH were selected after considering the agricultural activities and anthropogenic activities that have been taking place in the woreda, as they have a higher influence on changing the groundwater quality. Hence, this study area was chosen. The coordinates of these points were taken using a geographic positioning system (GPS), and the sampling point's locations are shown in Table 1.

The sampling points were selected based on existing well infrastructure within the study area, prioritizing operational wells across varying depths (shallow to deep aquifers) to capture vertical and horizontal heterogeneity in groundwater quality. Although the spatial distribution of wells appears linear (resembling a ‘rope-like’ pattern on the map), this alignment reflects the regional groundwater flow direction, following hydraulic gradients from recharge zones in elevated areas to discharge zones in lowland regions. This strategic placement allows systematic tracking of contaminant transport processes, such as advection and dispersion, along dominant flow paths. The contamination pressures considered in this study focused on two primary sources: agricultural activities and community wastewater. Agricultural zones contribute pollutants through the leaching of fertilizers and pesticides (e.g., nitrate and phosphate ⁠) into shallow aquifers, as well as microbial and organic contaminants from animal waste infiltration. Community wastewater, particularly from pit latrines, introduces pathogens (e.g., fecal coliforms), ammonium ⁠, and chloride Cl⁻ into the groundwater system.

The appropriateness of the groundwater for drinking purposes was evaluated using major ions concentrations (Ca²⁺, Mg²⁺, Na⁺, K⁺, Fe⁺, ⁠, ⁠, ⁠, F⁻, and Cl⁻) and significant physicochemical parameters pH, EC, and TDS which is used by many scholars to evaluate the suitability of groundwater for drinking purposes (Goodarzi et al. 2022; Chinthala et al. 2023; Kumar et al. 2024). Whether or not water is intended for home use, TDS and EC are crucial water quality parameters. The parameters standard that was given by WHO (2017) and ESA (2013) are shown in Table 2.

Table 2

Drinking water quality standard (ESA 2013; WHO 2017)

Parameter .	WHO standards (mg/L) .	Most desirable limits .	WHO maximum allowable limits .	Ethiopian standard .
PH	6.5–8.5	8.5	3	6.5–8.5
TDS	500–1,500	1,500	5	1,000
EC	300	1,000	3	400
	120	120	3	120
	200–400	400	3	250
Cl−	250	1,000	4	250
	11	45	5	50
F−	1.5	1.5	5	1.5
Ca2+	75	200	3	75
Mg2+	50	150	3	50
Na+	200	200	2	200
K+	12	12	2	1.5
Temperature	12–25	150	3	30
Fe	0.3	1	2	0.3
Turbidity (NTU)	5	5	5	5

Parameter .	WHO standards (mg/L) .	Most desirable limits .	WHO maximum allowable limits .	Ethiopian standard .
PH	6.5–8.5	8.5	3	6.5–8.5
TDS	500–1,500	1,500	5	1,000
EC	300	1,000	3	400
	120	120	3	120
	200–400	400	3	250
Cl−	250	1,000	4	250
	11	45	5	50
F−	1.5	1.5	5	1.5
Ca2+	75	200	3	75
Mg2+	50	150	3	50
Na+	200	200	2	200
K+	12	12	2	1.5
Temperature	12–25	150	3	30
Fe	0.3	1	2	0.3
Turbidity (NTU)	5	5	5	5

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The groundwater quality can be evaluated and rated using WQI which is the popular technique for assessing groundwater quality for drinking (Yogendra & Puttaiah 2008; Kahsay et al. 2019; Zeabraha et al. 2020; Wang et al. 2023; Pappaka et al. 2024). It is an arithmetic instrument that converts vast amounts of water quality data into a single, cumulatively determined number. The WQI yields a single number that represents the average water quality at a specific point in time, based on analytical values of physicochemical factors (Yogendra & Puttaiah 2008).

This WQI, often called the weighted arithmetic mean technique, was first proposed by Horton (1965) and Jacobs et al. (2016), which is a reflection of the combined impact of different quality measures on the water's overall quality. These WQIs have been used to assess the quality of the water in a certain location. Many researchers have employed this index in their work to create public policy and carry out initiatives to improve water quality and obtain accurate data on water quality (Yogendra & Puttaiah 2008; Aragaw & Gnanachandrasamy 2021; Tegegne et al. 2023).

Among different methods to calculate WQI, in this study, the weighted arithmetic water quality index (WAWQI) method was used due to it encompasses various physicochemical parameters of water quality parameter which makes the method more sophisticated.

In the case of this study, the computed value of IBE was equal to −2.24, which is within the acceptable limit of ±10%.

The results here are limited to the selected physicochemical parameters such as temperature, pH, EC, TDS, magnesium, calcium, sodium, chloride, nitrate, turbidity, iron, fluoride, potassium, sulfate, and bicarbonate are included which are essential for the determination of groundwater quality.

Some of the parameters that exceeded the WHO standard may be its source of erosion in the highland area of the mountain, geological rock interaction, and the fertilizer which is used by the farmers in the agricultural area.

The pH values of the woreda vary from slightly acidic to slightly alkaline. In most sampling sites, the pH of water lies within the WHO maximum allowable drinking water quality ranges and the draft Ethiopian drinking water guidelines, except W15 in the dry season and W4 and W5 in the wet season. The pH values of most natural water are in the range of 6.5–8.5. Therefore, about 10% of the samples are below the limit. This happened due to carbonate-rich formations like limestone/dolostone aquifers and silicate-rich formations like granite. The spatial variation map of pH shows that the groundwater of the study area is slightly acidic to alkaline. The pH values of all of the study areas fall in the range of the drinking water guideline value of WHO (2017), which is 6.0–8.5.

The samples of groundwater sources present in the study region of EC fell 100% in good class for the dry season and 13.33% in excellent class and 86.67% in good class for the wet season (Table 4).

Figure 7 shows that, in this study area, the calcium content in the wells studied in general shows significant seasonal variations. Consequently, concerning this parameter, the water quality of the study area of most considered sites is acceptable. However, for Ca²⁺ concentration in the study area, about 6.67% was unsuitable for drinking.

The remaining samples have very low fluoride contents, and the nature of rocks and soil types located around the studied area does not have enough fluoride ions. And the area does not have a risk of fluoride contamination.

WQI is an important tool for policymakers and water resource managers, simplifying complex water quality data into an easily interpretable score, enabling informed decision-making and targeted interventions. It enables us to classify the water into excellent, good, poor, and unsuitable. It also plays a vital role in enhancing public awareness and community engagement by making water quality data more accessible, encouraging local participation in pollution prevention, and promoting household-level treatment solutions. By integrating WQI into policy frameworks, intervention programs, and climate resilience planning, decision-makers can ensure sustainable groundwater management and improved public health outcomes, particularly in vulnerable regions. A study by Sharma et al. (2020) and Rana et al. (2018) in India assessed the impact of leachate pollution on the groundwater quality and assessed the pollution potential of leachate from non-engineered landfill sites and its effect on groundwater quality, respectively.

The variations of physicochemical characteristics and the WQI of the groundwater in various places around the study area are presented in Table 5. The groundwater quality shows variations from well to well, attributed to the surface and subsurface features. As shown in the previous figure, spatial interpolation of ArcGIS using the WQI parameter was utilized for plotting a digital map to describe the suitability of water for human needs in the study area. These maps represent an efficient tool for managing the water quality and minimizing the negative impacts on the ambient environment.

While WQI is a valuable tool for simplifying groundwater quality assessment, it has several limitations, including the loss of detailed information, and subjectivity in parameter selection and weighting. Additionally, WQI may fail to detect emerging contaminants such as heavy metals, pesticides, and pharmaceuticals, and does not directly correlate with human health risks. To overcome these challenges, complementary approaches should be integrated, such as multivariate statistical analysis (e.g., principal component analysis (PCA), cluster analysis) to identify pollution sources, hydrochemical and isotopic analysis to understand contamination pathways, and microbial testing to detect biological contaminants.

As shown in Tables 6 and 7, in the WQI in both dry and wet seasons, 80% of the water fell in the excellent range, and 20% fell in the good range. Therefore, all the samples were suitable for drinking purposes. The classification of the WQI was obtained from the works of literature (Goodarzi et al. 2022). A similar study by Asmamaw & Debie (2023) is in line with this study and uses WQI to evaluate the groundwater quality in Bahir Dar city, Northern Ethiopia, for drinking purposes.

The groundwater quality assessment for drinking purposes conducted in Damot Gale Woreda has provided valuable insights into the physicochemical characteristics of the region's groundwater and its suitability for drinking purposes. The analysis revealed significant seasonal variations in key water quality parameters, highlighting the influence of natural geochemical processes and anthropogenic activities on groundwater composition. While most parameters remained within the acceptable limits set by the WHO and Ethiopian drinking water standards, certain parameters, including pH, iron, fluoride, bicarbonate, turbidity, potassium, and temperature, exceeded permissible levels in some water sources. These deviations suggest localized contamination, which may be primarily due to geological formations, agricultural runoff, and natural water–rock interactions.

The WQI classification indicated that a majority of the groundwater sources fall within the ‘excellent’ to ‘good’ categories, signifying their general suitability for drinking. However, the elevated iron and fluoride levels in certain wells could pose long-term health risks, such as dental and skeletal fluorosis, if not properly managed. Additionally, high turbidity levels in some groundwater samples may indicate the presence of suspended particles and microbial contaminants, further emphasizing the need for proper treatment and regular monitoring.

To safeguard public health and ensure sustainable groundwater use, it is imperative to implement effective water treatment measures, including filtration and difluorination techniques where necessary. Source protection strategies, such as controlled agricultural practices, wellhead protection zones, and community awareness programs, should also be prioritized. Furthermore, continuous monitoring and periodic assessment of groundwater quality are essential to track changes over time and mitigate emerging contamination risks.

In conclusion, while groundwater remains a vital source of drinking water in Damot Gale Woreda, proactive management and intervention strategies are crucial for maintaining its quality. The findings of this study can serve as a foundation for policymakers, water resource managers, and local communities to take evidence-based actions aimed at improving water safety and promoting sustainable groundwater utilization in the region. For future research, since the WQI alone does not identify the potential sources of contamination, further studies should be conducted using multivariate statistical analysis (e.g., PCA, cluster analysis) to determine pollution sources, hydrochemical and isotopic analysis to understand contamination pathways, and microbial testing to detect biological contaminants.

This work was not supported financially by any institute or organization.

The submitted work is original and does not have been published elsewhere in any form or language (partially or in full).

T.T., M.B., and H.G.: investigation, conceptualization, resources, and visualization; T.T. and H.G.: formal analysis, methodology, ANOVA, laboratory, and writing – original draft preparation; M.B. and T.T.: writing – review and editing. All authors read and approved the final manuscript.

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

The authors declare there is no conflict.