Assessing the quality of the Kulfo River water for domestic use in the Limat area, Arba Minch Open Access

CCME water quality index, domestic water use, Kulfo River, physicochemical parameters, total and fecal coliforms, water quality assessment

Access to safe drinking water is crucial for human health, but many regions struggle with water scarcity and contamination. In the Limat area, these issues have led to significant health concerns, prompting the evaluation of the available water sources. This study aimed to assess the quality of Kulfo River water for domestic use. Water samples were collected from three sites during the dry and wet seasons of 2022 and analyzed according to APHA (2017) standards. The water suitability for drinking was determined using the CCME water quality index (WQI). While most parameters were within WHO and Ethiopian standards, significant deviations in turbidity were observed, ranging from 25.5 ± 3.54 to 88.2 ± 5.94 NTU, exceeding the 5 NTU limit. Total coliform ranged from 337.5 ± 17.68 to 1275 ± 388.09 counts/100 mL, and fecal coliform ranged from 212.5 ± 17.68 to 1225 ± 106.07 counts/100 mL, both far above acceptable limits. This contamination, likely from sanitation activities, animal waste, and agricultural runoff, suggests that while some parameters are acceptable, high turbidity and coliform levels make water unsafe for domestic use without treatment. Considerable treatment and pollution control are essential to ensure the safety of water.

HIGHLIGHTS

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Water quality assessment: The Kulfo River was evaluated for domestic use with samples from the dry and wet seasons in 2022.
High turbidity: Turbidity (25.5–88.2 NTU) and coliforms (212.5–1,275/100 mL) exceed WHO standards.
Microbial risk: Site 1 was classified as fair (WQI: 68.37), and sites 2 and 3 as marginal.
Treatment needed: Significant treatment is required for domestic use, along with better pollution monitoring in the Limat area.

INTRODUCTION

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Water is an indispensable resource that is essential for the survival of all living organisms. Access to clean and sufficient water is directly linked to human health, socioeconomic development, and environmental sustainability (WHO/UNICEF 2019; Mishra et al. 2021). However, nearly a billion people globally lack access to clean and adequate water, forcing many to rely on unsafe water sources (Kidanie 2015; Duressa et al. 2019; WHO/UNICEF 2019). This global water crisis has severe consequences, particularly in low-income countries where waterborne diseases account for nearly 80% of all illnesses (Yasin et al. 2015; Chan et al. 2021). In Ethiopia, ensuring reliable and safe water for domestic use remains a significant challenge exacerbated by rapid population growth, urbanization, and environmental degradation (Abbas & Hassan 2018). Rivers such as the Kulfo River, located around the Limat area of the Arba Minch, play a critical role in providing water for domestic, agricultural, and industrial purposes, as well as supporting ecosystems. However, the declining water quality of the Kulfo River, driven by increasing population pressure, urbanization, and environmental degradation, raises concerns regarding its suitability for domestic use. Despite the importance of the river, previous studies have predominantly focused on hydrology, erosion, and sediment dynamics (Tadelech 2015; Jothimani et al. 2020; Ojha et al. 2020; Yisehak et al. 2020), leaving a significant gap in studies assessing water quality, particularly for domestic use in the context of rapid population growth and strained water infrastructure. Evaluating water quality through the analysis of physical, chemical, and biological parameters is crucial for determining the treatment processes required to meet standards for domestic use (Meinzinger et al. 2009; Muralitharan et al. 2021). Water shortages in the town of Arba Minch are already acute, and the demand for safe drinking water consistently exceeds supply. The contributing factors include rural-to-urban migration, urbanization, lifestyle changes, and economic growth. Current water supply coverage is only 56%, with daily per capita consumption averaging less than 30 L, far below the national target of 80 L/person, as outlined in Ethiopia's Second Growth and Transformation Plan (Abebe et al. 2014; MoWIE 2019). This disparity has serious public health implications, leading to poor sanitation, hygiene, and the spread of waterborne diseases such as diarrhea, typhoid, and amebiasis, particularly among vulnerable populations such as children under 5 years of age. Recognizing the critical need for clean water access, this study aimed to evaluate the water quality of the Kulfo River, with a specific focus on its suitability for domestic use in the Limat area. By analyzing key physicochemical and biological parameters, such as pH, electrical conductivity (EC), total dissolved solids (TDS), turbidity, dissolved oxygen (DO), biological oxygen demand (BOD₅), chemical oxygen demand (COD), and major ions (Ca²⁺, Mg²⁺, Na²⁺, K²⁺, Cl⁻, F⁻, ⁠, and ⁠), total iron, manganese, and total and fecal coliforms (FC), during both wet and dry seasons, this research seeks to identify the extent of pollution and propose appropriate water treatment processes. The findings will not only provide insights into the current state of the Kulfo River, but also offer actionable recommendations to address water scarcity and improve public health in the region.

MATERIALS AND METHODS

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General description of the study area

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The Kulfo River is a perennial river with minor tributary streams and gullies that run 30 km through southern Ethiopia. The average annual temperature and rainfall were 30°C and 907.07 mm, respectively. The upstream portion of the catchment area is utilized for farming and grazing; typically, the catchment area's crops include maize, sweet potatoes, cotton, bananas, and sugarcane (Wagesho 2014; Tadele & Förch 2007). A map of the study area is presented in Figure 1.

Figure 1

Description of the study area map.

Materials/tools

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Some of the materials and apparatus used for the water quality analysis are listed in Table 1 and in Figure 2. The water quality parameters selected in this experiment were determined using the techniques outlined in Table 2. All laboratory analyses were conducted following the American Public Health Association's standard procedures APHA (2017). The results of each analysis represent the mean of three replicate measurements.

Table 1

Materials used for this study

Details	Purpose of use	Significance
Laboratory equipment's and materials	Water quality analysis	Used for collection, storage, and analysis of the water sampling parameters
Icebox	Water quality analysis	Storage and preservation of the characteristic water samples to keep the water samples from changes in properties and contamination
HQ40d Multimeter	On-site water quality parameters analysis	Some of the parameters like temperature, pH, EC, DO, TDS, and salinity may lose their properties speedily with time or are very sensitive to time, so they were analyzed in situ as soon as the samples were collected
Landsat8 images, DEM ArcGIS 10.7	For LULC preparation, to identify the source and type of pollutants introduced in river	Showed the character of land-use or land-cover classes/features, generated watershed delineation, and extracted the stream networks or tributaries of the river
GPS	Record coordinates	Identified the sampling points’ locations

Details	Purpose of use	Significance
Laboratory equipment's and materials	Water quality analysis	Used for collection, storage, and analysis of the water sampling parameters
Icebox	Water quality analysis	Storage and preservation of the characteristic water samples to keep the water samples from changes in properties and contamination
HQ40d Multimeter	On-site water quality parameters analysis	Some of the parameters like temperature, pH, EC, DO, TDS, and salinity may lose their properties speedily with time or are very sensitive to time, so they were analyzed in situ as soon as the samples were collected
Landsat8 images, DEM ArcGIS 10.7	For LULC preparation, to identify the source and type of pollutants introduced in river	Showed the character of land-use or land-cover classes/features, generated watershed delineation, and extracted the stream networks or tributaries of the river
GPS	Record coordinates	Identified the sampling points’ locations

Note. Remark: The laboratory equipment's and materials were Turbidimeter, UV–vis spectrophotometer, flame photometer, analytical balance, dish, burette, pipette, furness, filter paper, petri dish, incubator, oven dry, distillation apparatus, measuring cylinder, beaker, sterilizer, icebox, bottles, dropper, dissector and so on. DEM, digital elevation model; GPS, global positioning system; LULC, land use land cover.

Table 2

Standard methods for laboratory water quality analysis

Parameter	Units	Method
Temperature	°C	Multimeter (Model HQ40d)
pH	—–	Multimeter (Model HQ40d)
EC	μS/cm	Multimeter (Model HQ40d)
DO	mg/L	Multimeter (Model HQ40d)
TDSs	mg/L	Multimeter (Model HQ40d)
Turbidity	NTU	Turbidity Meter
Total solids	mg/L	Gravimetric method
Total suspended solids (TSS)	mg/L	Gravimetric method
Total hardness	mg/L	EDTA titrimetric method
Calcium hardness	mg/L	EDTA titrimetric method
Magnesium hardness	mg/L	EDTA titrimetric method
Sodium (Na⁺)	mg/L	Flame photometer
Potassium (K⁺)	mg/L	Flame photometer
Chloride (Cl⁻)	mg/L	Argentometric method
Fluoride (F⁻)	mg/L	Spectrophotometer (580 nm)
Nitrate (⁠⁠)	mg/L	Phenol sulfonic acid (410 nm)
Sulfate (⁠⁠)	mg/L	UV–vis spectrophotometer (410 nm)
Total iron	mg/L	UV–vis spectrophotometer (480 nm)
Manganese (Mn²⁺)	mg/L	UV–vis spectrophotometer (530 nm)
BOD₅	mg/L	Winkler method
COD	mg/L	Open reflex method
TC	No./100 mL	Membrane filtration method (MFM)
FC	No./100 mL	Membrane filtration method (MFM)

Parameter	Units	Method
Temperature	°C	Multimeter (Model HQ40d)
pH	—–	Multimeter (Model HQ40d)
EC	μS/cm	Multimeter (Model HQ40d)
DO	mg/L	Multimeter (Model HQ40d)
TDSs	mg/L	Multimeter (Model HQ40d)
Turbidity	NTU	Turbidity Meter
Total solids	mg/L	Gravimetric method
Total suspended solids (TSS)	mg/L	Gravimetric method
Total hardness	mg/L	EDTA titrimetric method
Calcium hardness	mg/L	EDTA titrimetric method
Magnesium hardness	mg/L	EDTA titrimetric method
Sodium (Na⁺)	mg/L	Flame photometer
Potassium (K⁺)	mg/L	Flame photometer
Chloride (Cl⁻)	mg/L	Argentometric method
Fluoride (F⁻)	mg/L	Spectrophotometer (580 nm)
Nitrate (⁠⁠)	mg/L	Phenol sulfonic acid (410 nm)
Sulfate (⁠⁠)	mg/L	UV–vis spectrophotometer (410 nm)
Total iron	mg/L	UV–vis spectrophotometer (480 nm)
Manganese (Mn²⁺)	mg/L	UV–vis spectrophotometer (530 nm)
BOD₅	mg/L	Winkler method
COD	mg/L	Open reflex method
TC	No./100 mL	Membrane filtration method (MFM)
FC	No./100 mL	Membrane filtration method (MFM)

EDTA, ethylene diamine tetraacetic acid.

Figure 2

Iceboxes and multimeter instruments used during field sampling collection.

Sampling collection techniques

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Sampling site selection: A thorough preliminary assessment was conducted to identify the most representative water sampling sites along the Kulfo River in alignment with the objectives of the study, potential pollution sources, land use, and human influence. Three sampling locations were identified: upstream, midstream, and downstream of the Limat Area, focusing on the river's major tributaries. The upstream site (Location 1) exhibited minimal human interference and was surrounded by cropland, forest, grassland, and scrubland. The midstream site (Location 2) similarly showed limited human activity, with the area characterized by forest, grassland, agricultural, and livestock-related practices. In contrast, the downstream site (Location 3) experienced slightly greater human intervention, influenced by sanitation practices, and intensified agricultural activities. The site characteristics are shown in Figure 3.

Figure 3

LULC and locations of sampling points of the Kulfo River catchment.

Sampling collection method: In this study, composite water samples were collected from well-mixed sections of the river, 30 cm below the surface, using 2 L bottles for physicochemical tests and 100 mL sterilized bottles for microbiological tests, as shown in Figure 4. Sample bottles were triple-rinsed with raw water, and laboratory instruments were calibrated according to APHA (2017) standards. Water samples were collected on four dates in 2022 (14 February, 19 March, 27 April, and15 September) and analyzed at the Arba Minch University water quality laboratory. Results are reported as mean ± standard deviation, using Microsoft Excel 2019, and presented in tables, charts, and graphs.

Figure 4

River water samples collection for physicochemical and microbiological analysis. (a = sampling collection in April, b = sampling collection in September, c = samplers for physicochemical analysis, d = samplers for microbiological analysis.)

Storage, preservation, and transportation of samples: Physicochemical water samples were preserved in glass or polyethylene bottles and stored in an icebox at 3–4 °C to prevent constituent loss. For iron, manganese, and other ions, samples were stored in plastic bottles with nitric acid (HNO₃) at pH < 2.0, to avoid ion loss. Microbiological samples were immediately placed in a light-proof icebox for rapid cooling. Physicochemical and microbiological samples were stored in a refrigerator and analyzed within 48 h, whereas bacteriological tests were conducted within 6 h. The transport to the laboratory was facilitated by Bajaj, as shown in Figure 5.

Figure 5

Sampling preservation and transportation to the laboratory for analysis.

Before the analysis, the instruments were pre-calibrated with a buffer solution and rinsed with deionized water. Temperature, pH, EC, DO, TDS, and salinity were measured in situ using a multimeter immediately after sampling owing to their time sensitivity, as shown in Figure 6.

Figure 6

On-site analyzed water quality parameters using a multimeter instrument. a = multimeter, b = parameters analysis, c = recording results.

Water Quality Index (CCME WQI): The WQI was selected based on its widespread use globally, including in Ethiopia, its compatibility with various water uses, and the availability of required data. The Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI) model has been applied to several surface water bodies worldwide (Lumb et al. 2006; Abbasi & Abbasi 2012; Galal et al. 2017; Bilgin 2018). In this study, the CCME WQI was used to classify water pollution at the selected sampling sites. It is expressed as:

(1)

where F₁ represents ‘scope’: the percentage of variables that exceed the guideline or the number of variables that do not meet the specified objectives. It is expressed as follows:

(2)

F₂ represents ‘frequency’: this is the percentage of individual test values within each variable that do not meet the guideline or objective values (failed tests). It is calculated as follows:

(3)

F₃ represents ‘amplitude’, this measures how much a failed test exceeds the guideline or how test values deviate from their objectives. The amplitude is calculated using an asymptotic function that scales the normalized sum of excursions (nse) of test values from objectives, yielding a value between 0 and 100 as follows:

(4)

The nse was calculated as follows:

(5)

If a test value falls below the objective value; the excursion for that value is calculated as follows:

(6)

Conversely, if the test value exceeds the objective value, then the excursion value is calculated as follows:

(7)

The constant value of 1.732 is a scaling factor that is used as a normalizing factor (F₁, F₂, and F₃) to ensure the resultant WQI varies in the range of 0–100, where 0 denotes the ‘worst’ water quality and 100 the ‘best’ (Canadian Council of Ministers of the Environment 2001; Radeva & Seymenov 2020). CCME WQI Categorization is presented in Table 3.

Table 3

CCME WQI categorization

WQI value	Ranks	Characteristics
95–100	Excellent	All measurements within objective virtually all the time Conditions very closely to pristine water quality levels The virtual absence of threat or impairment
80–94	Good	Conditions rarely deviate from natural or desirable levels A minor degree of threatened or impaired to water quality
65–79	Fair	Conditions sometimes deviate from natural desirable levels Water quality is occasionally threatened or impaired
45–64	Marginal	Conditions often deviate from natural or desirable levels Water quality is frequently threatened or impaired
0–44	Poor	Conditions usually deviate from natural or desirable levels Water quality is almost always threatened or impaired

WQI value	Ranks	Characteristics
95–100	Excellent	All measurements within objective virtually all the time Conditions very closely to pristine water quality levels The virtual absence of threat or impairment
80–94	Good	Conditions rarely deviate from natural or desirable levels A minor degree of threatened or impaired to water quality
65–79	Fair	Conditions sometimes deviate from natural desirable levels Water quality is occasionally threatened or impaired
45–64	Marginal	Conditions often deviate from natural or desirable levels Water quality is frequently threatened or impaired
0–44	Poor	Conditions usually deviate from natural or desirable levels Water quality is almost always threatened or impaired

RESULTS AND DISCUSSIONS

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Analyzed physicochemical and biological drinking water quality parameters

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This study analyzed 25 physicochemical and biological parameters; the detailed results are provided in Table 4.

Table 4

Statistical summary of drinking water quality parameters along with the sampling points

	Sampling point name (Code = Sp) and results of field measurements
	Sp₁ mean values		Sp₂ mean values		Sp₃ mean values		P.Limit
	Dry	Wet	Dry	Wet	Dry	Wet	WHO
Parameters	ū ± ð	ū ± ð	ū ± ð	ū ± ð	ū ± ð	ū ± ð
Temp, (°C)	23.5 ± 0.71	21.1 ± 0.43	24.45 ± 0.07	22.55 ± 1.47	24.7 ± 0.14	22.65 ± 1.20	—-
DO, (mg/L)	6.72 ± 0.18	6.995 ± 0.02	6.6 ± 0.06	6.9 ± 0.02	6.5 ± 0.09	6.78 ± 0.15	> 4
EC, (μS/cm)	817 ± 8.46	495.5 ± 23.34	820.5 ± 19.1	516 ± 25.46	828 ± 15.56	526.5 ± 14.85	Nil
pH	8.46 ± 0.10	8.11 ± 0.10	8.68 ± 0.04	7.99 ± 0.23	8.66 ± 0.14	7.74 ± 0.66	6.5–8.5
TDS, (mg/L)	399.5 ± 12.02	257.5 ± 12.02	407 ± 14.14	262 ± 15.56	408 ± 18.39	265.5 ± 13.44	—-
Salinity, (%)	0.4 ± 0.02	0.255 ± 0.01	0.4 ± 0.02	0.255 ± 0.01	0.4 ± 0.01	0.255 ± 0.01	Nil
Turbidity, (NTU)	25.5 ± 3.54	85.6 ± 2.69	30.0 ± 4.24	86.85 ± 3.04	32.5 ± 4.95	88.2 ± 5.94	5
Total solid (mg/L)	535 ± 11.32	3,878 ± 98.99	535 ± 7.07	3,510 ± 554.4	535 ± 15.56	3,398.5 ± 355.7	—-
TSS, (mg/L)	135.5 ± 23.34	3,620.5 ± 86.98	128 ± 7.07	3,248 ± 538.8	127 ± 2.83	3,133 ± 342.24	—
BOD_5, (mg/L)	4.09 ± 0.20	2.39 ± 0.27	4.55 ± 0.28	3.04 ± 0.16	5.99 ± 0.66	3.51 ± 0.44	< 2
COD, (mg/L)	9.5 ± 0.71	5.5 ± 0.71	8.5 ± 1.71	6.0 ± 1.42	13.0 ± 1.42	8.5 ± 0.71	—–
T.A, (mg/L)	160 ± 11.32	92 ± 5.66	171 ± 18.39	98 ± 14.14	173.5 ± 14.85	98 ± 19.8	200
T.H, (mg/L)	58 ± 2.83	68 ± 5.66	58.5 ± 2.12	72 ± 5.66	64 ± 5.66	76 ± 5.66	200
Ca²⁺, (mg/L)	31.28 ± 1.02	44.66 ± 6.58	31.85 ± 0.21	42 ± 2.83	43.69 ± 15.93	43 ± 4.24	100
Mg^2+, (mg/L)	26.72 ± 1.81	23.35 ± 12.24	26.65 ± 1.91	30 ± 2.83	20.31 ± 10.26	33 ± 1.42	—
Na⁺, (mg/L)	24.6 ± 1.27	18.55 ± 1.35	25.1 ± 1.27	18.6 ± .99	26.05 ± 0.92	20.14 ± 0.23	200
K⁺, (mg/L)	2.45 ± 0.07	1.8 ± 0.14	1.95 ± 0.07	1.7 ± 0.14	2.15 ± 0.07	1.45 ± 0.21	Nil
Cl⁻, (mg/L)	46.72 ± 1.13	21.4 ± 2.02	44.58 ± 0.93	21.41 ± 2.04	33.76 ± 2.57	21.52 ± 2.19	250
F⁻, (mg/L)	0.34 ± 0.01	0.24 ± 0.02	0.39 ± 0.02	0.2 ± 0.09	0.36 ± 0.03	0.21 ± 0.08	1.5
SO₄²⁻, (mg/L)	20.44 ± 1.69	6.40 ± 1.61	17.81 ± 1.13	6.89 ± 1.92	16.36 ± 0.22	7.03 ± 1.75	250
⁠, (mg/L)	0.09 ± 0.01	0.47 ± 0.05	0.09 ± 0.01	0.48 ± 0.05	0.01 ± 0.01	0.51 ± 0.01	50
FC, (No./100 mL)	212.5 ± 17.68	633.5 ± 47.38	450 ± 70.71	1,125 ± 176.8	862.5 ± 194.46	1,225 ± 106.07	MND
TC, (No./100 mL)	337.5 ± 17.68	641.5 ± 153.44	533.5 ± 94.1	1,225 ± 247.5	1,016 ± 260.22	1,275 ± 388.91	MND
T.iron, (mg/L)	0.06 ± 0.01	0.09 ± 0.02	0.05 ± 0.00	0.08 ± 0.01	0.07 ± 0.00	0.08 ± 0.01	0.3
Mn²⁺, (mg/L)	ND	ND	ND	ND	ND	ND	0.1

	Sampling point name (Code = Sp) and results of field measurements
	Sp₁ mean values		Sp₂ mean values		Sp₃ mean values		P.Limit
	Dry	Wet	Dry	Wet	Dry	Wet	WHO
Parameters	ū ± ð	ū ± ð	ū ± ð	ū ± ð	ū ± ð	ū ± ð
Temp, (°C)	23.5 ± 0.71	21.1 ± 0.43	24.45 ± 0.07	22.55 ± 1.47	24.7 ± 0.14	22.65 ± 1.20	—-
DO, (mg/L)	6.72 ± 0.18	6.995 ± 0.02	6.6 ± 0.06	6.9 ± 0.02	6.5 ± 0.09	6.78 ± 0.15	> 4
EC, (μS/cm)	817 ± 8.46	495.5 ± 23.34	820.5 ± 19.1	516 ± 25.46	828 ± 15.56	526.5 ± 14.85	Nil
pH	8.46 ± 0.10	8.11 ± 0.10	8.68 ± 0.04	7.99 ± 0.23	8.66 ± 0.14	7.74 ± 0.66	6.5–8.5
TDS, (mg/L)	399.5 ± 12.02	257.5 ± 12.02	407 ± 14.14	262 ± 15.56	408 ± 18.39	265.5 ± 13.44	—-
Salinity, (%)	0.4 ± 0.02	0.255 ± 0.01	0.4 ± 0.02	0.255 ± 0.01	0.4 ± 0.01	0.255 ± 0.01	Nil
Turbidity, (NTU)	25.5 ± 3.54	85.6 ± 2.69	30.0 ± 4.24	86.85 ± 3.04	32.5 ± 4.95	88.2 ± 5.94	5
Total solid (mg/L)	535 ± 11.32	3,878 ± 98.99	535 ± 7.07	3,510 ± 554.4	535 ± 15.56	3,398.5 ± 355.7	—-
TSS, (mg/L)	135.5 ± 23.34	3,620.5 ± 86.98	128 ± 7.07	3,248 ± 538.8	127 ± 2.83	3,133 ± 342.24	—
BOD_5, (mg/L)	4.09 ± 0.20	2.39 ± 0.27	4.55 ± 0.28	3.04 ± 0.16	5.99 ± 0.66	3.51 ± 0.44	< 2
COD, (mg/L)	9.5 ± 0.71	5.5 ± 0.71	8.5 ± 1.71	6.0 ± 1.42	13.0 ± 1.42	8.5 ± 0.71	—–
T.A, (mg/L)	160 ± 11.32	92 ± 5.66	171 ± 18.39	98 ± 14.14	173.5 ± 14.85	98 ± 19.8	200
T.H, (mg/L)	58 ± 2.83	68 ± 5.66	58.5 ± 2.12	72 ± 5.66	64 ± 5.66	76 ± 5.66	200
Ca²⁺, (mg/L)	31.28 ± 1.02	44.66 ± 6.58	31.85 ± 0.21	42 ± 2.83	43.69 ± 15.93	43 ± 4.24	100
Mg^2+, (mg/L)	26.72 ± 1.81	23.35 ± 12.24	26.65 ± 1.91	30 ± 2.83	20.31 ± 10.26	33 ± 1.42	—
Na⁺, (mg/L)	24.6 ± 1.27	18.55 ± 1.35	25.1 ± 1.27	18.6 ± .99	26.05 ± 0.92	20.14 ± 0.23	200
K⁺, (mg/L)	2.45 ± 0.07	1.8 ± 0.14	1.95 ± 0.07	1.7 ± 0.14	2.15 ± 0.07	1.45 ± 0.21	Nil
Cl⁻, (mg/L)	46.72 ± 1.13	21.4 ± 2.02	44.58 ± 0.93	21.41 ± 2.04	33.76 ± 2.57	21.52 ± 2.19	250
F⁻, (mg/L)	0.34 ± 0.01	0.24 ± 0.02	0.39 ± 0.02	0.2 ± 0.09	0.36 ± 0.03	0.21 ± 0.08	1.5
SO₄²⁻, (mg/L)	20.44 ± 1.69	6.40 ± 1.61	17.81 ± 1.13	6.89 ± 1.92	16.36 ± 0.22	7.03 ± 1.75	250
⁠, (mg/L)	0.09 ± 0.01	0.47 ± 0.05	0.09 ± 0.01	0.48 ± 0.05	0.01 ± 0.01	0.51 ± 0.01	50
FC, (No./100 mL)	212.5 ± 17.68	633.5 ± 47.38	450 ± 70.71	1,125 ± 176.8	862.5 ± 194.46	1,225 ± 106.07	MND
TC, (No./100 mL)	337.5 ± 17.68	641.5 ± 153.44	533.5 ± 94.1	1,225 ± 247.5	1,016 ± 260.22	1,275 ± 388.91	MND
T.iron, (mg/L)	0.06 ± 0.01	0.09 ± 0.02	0.05 ± 0.00	0.08 ± 0.01	0.07 ± 0.00	0.08 ± 0.01	0.3
Mn²⁺, (mg/L)	ND	ND	ND	ND	ND	ND	0.1

T.A, total Alkalinity as CaCO₃; T.H, total hardness as CaCO₃; P.Limit, permissible limit; ND, not detected; MND, must not be detected.

Temperature: On-site evaluation of water temperature was conducted immediately after sample collection because of timely fluctuations that affect pH, DO, and other parameters. As shown in Table 4 and Figure 7, temperatures ranged from 23.5 ± 0.71 to 24.7 ± 0.14 °C during the dry season and from 21.1 ± 1.43 to 22.65 ± 1.20 °C in the wet season. Freshwater is considered safe to drink within the temperature range of 10–15 °C. Notably, temperatures were consistently higher during the dry season, with values exceeding 15 °C, posing risks to water quality and affecting chemical reactions and gas solubility (WHO 2011; Terzi & Verep 2012).

Figure 7

Temperatures at water sampling points along the Kulfo River.

Turbidity: The cloudiness of water was measured by assessing light scattering. According to the WHO and Ethiopian standards, turbidity in freshwater should not exceed 5 NTU for esthetic purposes, and ideally, it should be below 1 NTU for drinking. However, this study recorded turbidity values ranging from 25.5 ± 3.54 to 32.5 ± 4.95 NTU in the dry season and 85.6 ± 2.69 to 88.2 ± 5.94 NTU in the wet season (Table 4). These values are higher than previous studies, with Timotewos & Reddythota (2020) reporting 20.15 to 24.10 NTU in the dry season and Mekonnen & Desta (2017) recording 68 NTU in the wet season. Excessive turbidity is often associated with higher levels of microbiological contamination or pathogens, such as bacteria, viruses, and other parasites. The turbidity levels were significantly higher than the permissible limits for drinking, especially during the wet season (Figure 8). Upstream stations showed lower turbidity, while downstream stations had higher levels, likely due to agricultural and urban runoff and human activities, such as washing and soil erosion during heavy rainfall. High turbidity reduces the effectiveness of disinfectants and poses health risks by promoting bacterial growth (Lencha et al. 2021). This indicates the need for appropriate treatment technologies to make river water safe for drinking.

Figure 8

Mean turbidity and TSS values.

Total suspended solids (TSS): Particles retained during filtration ranged from 127 ± 2.83 to 135.5 ± 23.34 mg/L in the dry season and 3,133 ± 625.08 to 3,620.5 ± 86.98 mg/L in the wet season. TSS levels were significantly higher during the wet season, correlating with turbidity (Figure 8). These suspended particles are mainly due to agricultural erosion, livestock activities, and organic matter. No specific WHO or Ethiopian standards exist for TSS in drinking water, highlighting the need for proper treatment before domestic use.

Total dissolved solids: Are a key indicator of drinking water quality, comprising various inorganic salts such as sodium, calcium, magnesium, and sulfates that can affect water's taste and appearance (Olumana & Loiskandl 2015; Jin et al. 2021). The study found TDS levels ranging from 399.5 ± 12.02 to 408 ± 18.39 mg/L in the dry season and 257.5 ± 12.02 to 265.5 ± 13.44 mg/L in the wet season. According to WHO guidelines, the maximum TDS limit for drinking water is 1,000 mg/L, with levels below the ideal 600 mg/L. All sampling sites in both seasons recorded TDS levels in this study that were well within safe limits, indicating minimal exposure to geological formations, urban runoff, or industrial pollutants, making the river water safe for drinking in terms of TDS concentrations (Figure 9).

Figure 9

Mean TDS values along with the Kulfo River.

Total solids (TS): TS in water can affect both aquatic life and human health, as high levels retain heat and harm organisms, whereas low levels can limit growth due to nutrient deficiencies. In this study, TS concentrations ranged from 535 ± 11.32 to 535 ± 15.56 mg/L in the dry season, and from 2,798.5 ± 638.52 to 3,878 ± 99 mg/L in the wet season, indicating a significant increase during the rainy period (Figure 10). Previous studies by Teklemariam & Wenclawiak (2004) found TS values between 65 and 5,620 mg/L in the Kulfo River, indicating excessive solid accumulation. While TS does not pose direct health risks, it can cause esthetic concerns, requiring treatment for safe consumption.

Figure 10

TS along the Kulfo River.

pH: pH measures the concentration of free hydrogen ions, indicating the acidity or alkalinity of the water. Ideally, drinking water should have neutral pH, although slight variations are acceptable. In this study, pH levels ranged from 8.46 ± 0.12 to 8.66 ± 0.1 in the dry season and 7.74 ± 0.66 to 8.11 ± 0.12 in the wet season. WHO and Ethiopian guidelines set the permissible pH range for drinking water to 6.5–8.5. Most dry season samples exceeded this limit, except at one site, whereas wet season values fell within the acceptable range (Figure 11). Previous studies by Teklemariam & Wenclawiak (2004) reported pH values between 7.5 and 8.7, similar to this study. The slight increase in pH may be due to bicarbonate accumulation, soil composition, dissolved minerals, or pollutants. Although deviations from the ideal range can impact disinfection efficiency, they do not pose direct health risks to consumers. Overall, river water quality was slightly alkaline.

Figure 11

Mean values of pH along with the sampling sites.

Electrical conductivity: The EC measures the ability of water to carry an electric current, reflecting the concentration of soluble salts. In this study, EC values ranged from 817.5 ± 8.49 to 828 ± 15.56 μS/cm in the dry season and 495.5 ± 23.34 to 526.5 ± 14.85 μS/cm in the wet season (Table 4). According to WHO guidelines, an EC below 1,000 μS/cm is ideal for drinking water. All samples from both seasons were within this limit, with a higher EC recorded during the dry season (Figure 12). The results suggest that the river water contains moderate levels of dissolved ions, such as calcium chloride, sulfate, nitrate, sodium, and trace elements, making it suitable for drinking.

Figure 12

Mean EC values of the Kulfo River water samples.

Dissolved oxygen: DO is a crucial water quality parameter that influences the metabolic activities of aquatic organisms and indicates the health of water. In this study, DO concentrations ranged from 6.5 ± 0.09 to 6.72 ± 0.18 mg/L in the dry season and 6.78 ± 0.15 to 6.995 ± 0.021 mg/L in the wet season. Freshwater should maintain a DO level above 5 mg/L to support aquatic life, whereas higher levels in drinking water may cause pipe corrosion (Tafvizi 2022; Zheng et al. 2023). The results indicated that DO levels in the river were within the acceptable range in both seasons, showing a negative correlation with temperature (Figure 13). The absence of wastewater contamination likely contributed to the maintenance of these favorable DO levels.

Figure 13

DO level along with the Kulfo River water samples.

Salinity: Salinity measures the concentration of dissolved salts in water and is typically expressed in parts per thousand (ppt) or percentage. The freshwater salinity should be 0.5 mg/L or less. In this study, the average salinity values were 0.4 ± 0.01 in the dry season and 0.255 ± 0.01 in the wet season, as shown in Table 4. Salinity levels were consistent across sampling locations within each season but varied between seasons, with higher values during low-flow periods due to reduced water levels. Sudden changes in salinity can cause salinity shock, leading to high mortality rates in aquatic organisms. Salinity levels are closely related to chloride concentrations, which provide a direct measure of the salt content of water.

Total alkalinity (as

): This measures the ability of water to neutralize acids and absorb hydrogen ions without significantly changing its pH. In this study, the total alkalinity values ranged from 160 ± 11.31 to 173.5 ± 14.85 mg/L in the dry season and 92 ± 5.66 to 98 ± 19.80 mg/L in the wet season, as shown in Table 4 and Figure 14. These values were within the WHO and Ethiopian permissible limits of 200 mg/L for drinking water, with no significant health effects. The main contributors to alkalinity were carbonate, bicarbonate, and hydroxide compounds from calcium, magnesium, potassium, and sodium. Thus, Kulfo River water is safe for domestic use in terms of alkalinity.

Figure 14

Mean values of total alkalinity along with the sampling sites.

Total hardness: Total hardness (TH) in water is primarily determined by the concentration of calcium and magnesium salts. Total water hardness includes both carbonate and non-carbonate forms of hardness. Table 5 shows the classification of water based on the amount of dissolved salts, such as soft, moderate, hard, and very hard (Wimalawansa 2016). While excess hardness in water does not directly impact health, some studies have investigated its potential link to heart disease (Al-Badaii et al. 2013). The major contributors to water hardness are calcium and magnesium, which typically arise from contact between water and minerals, such as limestone, dolomite, and chalk. In this study, the TH of Kulfo River water ranged from 58 ± 2.83 to 64 ± 5.66 mg/L in the dry season and from 68 ± 5.66 to 76 ± 5.66 mg/L in the wet season. During the dry season, water was classified as moderately hard, whereas in the wet season, it was categorized as hard. These values are well within the WHO allowable limit of 300 mg/L for drinking water (Figure 15). The relatively lower hardness of surface water compared with groundwater is attributed to less contact with soil minerals and bedrock. Thus, from the perspective of TH, river water was deemed acceptable for drinking.

Table 5

Water hardness categories based on the amount of dissolved salts

Water hardness	Category	Range (mg/L)
Soft	Low hardness	0–60
Moderately hard	Medium hardness	61–120
Hard	High hardness	121–180
Very hard	Very high hardness	>180

Water hardness	Category	Range (mg/L)
Soft	Low hardness	0–60
Moderately hard	Medium hardness	61–120
Hard	High hardness	121–180
Very hard	Very high hardness	>180

Source: (Wimalawansa 2016).

Figure 15

Mean concentration of Ca2+, Mg 2+ and TH as CaCo3 in both seasons.

Mean concentration of Ca²⁺, Mg ²⁺ and TH as CaCo₃ in both seasons.

The study also analyzed calcium and magnesium, which directly contributed to the TH. Calcium concentrations ranged from 31.28 ± 1.02 to 43.69 ± 15.93 mg/L in the dry season and 42 ± 2.83 to 44.66 ± 6.59 mg/L in the wet season, all within the WHO guideline of 100 mg/L for drinking water. Magnesium concentrations ranged from 26.72 ± 1.81 to 20.31 ± 10.27 mg/L in the dry season and 23.35 ± 12.24 to 33 ± 1.42 mg/L in the wet season, staying within the Ethiopian standard limit of 50 mg/L (Figure 15). Excessive magnesium can have a laxative effect, but the recorded values are within safe limits. The findings on calcium and magnesium hardness closely align with studies by Timotewos & Reddythota (2020) and Teklemariam & Wenclawiak (2004).

Sodium (Na⁺) is a highly reactive metal that is naturally found in combination with other elements, often as sodium chloride. In the human body, sodium plays a vital role in maintaining water balance; however, excessive sodium chloride in drinking water can lead to heart disease and kidney issues. In this study, sodium concentrations ranged from 24.6 ± 1.27 to 26.05 ± 1.92 mg/L in the dry season and 18.55 ± 1.35 to 20.14 ± 0.24 mg/L in the wet season, well below the WHO guideline of 200 mg/L for safe drinking water (see Figure 16). These results are consistent with those of previous research, indicating that the sodium content of river water is within the safe limits.

Figure 16

Mean concentration of Na⁺ and K⁺ along with the sampling points.

Potassium (K⁺) is one of the most abundant elements in the Earth's crust and is typically bound to other compounds because its minerals are largely insoluble in water. The study found potassium levels between 1.95 ± 0.07 and 2.45 ± 0.07 mg/L in the dry season and 1.45 ± 0.21 to 1.8 ± 0.14 mg/L in the wet season, all within the WHO-recommended maximum limit of 12 mg/L for drinking water (Figure 16). Moderate K⁺ levels are likely due to minimal agricultural runoff and limited anthropogenic influence. These findings suggest that river water is suitable for drinking in terms of both sodium and potassium contents.

Chloride (Cl⁻): the chloride levels in water are closely related to the sodium content. In this study, chloride levels ranged from 33.76 ± 2.57 to 46.72 ± 1.13 mg/L during the dry season and 21.4 ± 2.02 to 21.52 ± 2.19 mg/L in the wet season, as presented in Table 4 and Figure 17. All the results were within the WHO limits for drinking water. Similar results were reported by Teklemariam & Wenclawiak (2004) and Mekonnen & Desta (2017), though Timotewos & Reddythota (2020) recorded higher values in the Kulfo River. Elevated chloride can cause a salty taste and health issues, often originating from sewage, animal waste, or saline water. These findings indicate that river water is free from sewage pollution and is safe for drinking.

Figure 17

Mean concentration Cl− and SO42− along with sampling sites of the Kulfo River.

Mean concentration Cl⁻ and SO₄²⁻ along with sampling sites of the Kulfo River.

Sulfates: Common in groundwater, they can cause bad taste and laxative effects in drinking water when present in high concentrations. In this study, sulfate levels ranged from 16.36 ± 0.22 to 20.44 ± 1.69 mg/L in the dry season and 6.4 ± 1.61 to 7.03 ± 1.75 mg/L in the wet season, as shown in Figure 17, well within the WHO's 250 mg/L limit. Both chloride and sulfate levels indicate that water is suitable for drinking without health concerns.

Fluoride (F⁻): Elevated levels of drinking water can pose health risks. Excess fluoride can cause dental and skeletal problems, although it is more common in groundwater. In this study, fluoride levels ranged from 0.34 ± 0.01 to 0.39 ± 0.02 mg/L in the dry season and 0.21 ± 0.08 to 0.24 ± 0.02 mg/L in the wet season – well below WHO's safe drinking water limit of 1.5 mg/L as shown in Figure 18. This low concentration is beneficial for preventing dental cavities.

Figure 18

Mean concentration of fluoride and nitrate along with sampling sites.

Nitrate (⁠⁠), formed through the oxidation of organic nitrogen, can be harmful if it exceeds safe levels, particularly in infants and pregnant women. However, nitrate levels in the water samples were minimal, ranging from 0.09 ± 0.00 to 0.01 ± 0.00 mg/L in the dry season and 0.47 ± 0.05 to 0.51 ± 0.01 mg/L in the wet season. These values are far below the WHO limit of 50 mg/L, indicating that the water is safe from agricultural runoff, domestic waste, and industrial pollutants. Therefore, both fluoride and nitrate concentrations in Kulfo River water are safe for drinking purposes, as shown in Figure 18.

Biochemical oxygen demand: Measures the oxygen needed to break down organic matter in water using microorganisms such as bacteria. This indicates the amount of biodegradable material present in the water samples. In this study, BOD₅ values ranged from 4.09 ± 0.21 to 5.99 ± 0.66 mg/L in the dry season and from 2.39 ± 0.27 to 3.51 ± 0.44 mg/L in the wet season after 5 days of incubation at 20 °C (see Table 4). Unpolluted freshwater usually has BOD₅ values of 2 mg/L or less (Muhammad et al. 2019; Moussa et al. 2022). A higher BOD₅ indicates more decomposable organic matter, leading to increased bacterial growth and decreased DO in water. BOD₅ was slightly higher in the dry season due to the lower water volume and higher organic accumulation (see Figure 19).

Figure 19

Mean value of BOD5 and COD along with sampling sites.

Mean value of BOD₅ and COD along with sampling sites.

Chemical oxygen demand: the oxygen is required to oxidize all organic matter in the water using chemicals. It is often used to assess industrial or domestic waste, as drinking water should be free of organic material. In this study, COD values ranged from 8.5 ± 3.71 to 13 ± 1.42 mg/L in the dry season and 5.5 ± 0.71 to 8.5 ± 0.71 mg/L in the wet season. Generally, unpolluted freshwater has COD values of ≤ 10 mg/L (Nasir et al. 2016). The findings suggest slight pollution in the Kulfo River water, particularly at sampling point 3 in the dry season, likely due to hygiene activities and animal waste. Efficient treatment is required before this water can be used for drinking. As shown in Figure 19, the COD and BOD₅ were positively correlated.

Iron and manganese: iron and manganese are common metals found in freshwater and are among the most abundant elements in Earth's crust. Drinking water quality guidelines for these metals are primarily set for esthetic reasons. High concentrations of Fe and Mn can cause brown and black stains on laundry, plumbing fixtures, and sinks. They can also create black sludge when reacting with beverages, such as tea and coffee, negatively affecting taste and appearance. In this study, iron levels in the sampled water ranged from 0.06 ± 0.01 to 0.07 ± 0.01 mg/L in the dry season and from 0.08 ± 0.01 to 0.09 ± 0.02 mg/L in the wet season. These values were within the WHO and Ethiopian drinking water standards of 0.3 mg/L (see Figure 20). Conversely, Mn was not detected at any sampling point during either season, indicating that Mn ions were absent in the water. Elevated Mn levels in river waters are typically linked to industrial activities (Tandon & Kumar 2015). Therefore, the concentrations of iron and manganese in Kulfo River water do not pose a significant risk to drinking water users.

Figure 20

Mean concentrations of total iron along with sampling sites.

Total and fecal coliforms: in this study, the analyzed results for FC and total coliforms (TC) showed counts ranging from 212.5 ± 17.68 to 862.5 ± 194.46 counts/100 mL in the dry season and 633.5 ± 47.38 to 1,225 ± 106.07 counts/100 mL in the wet season. Similarly, the TC values ranged from 337.5 ± 17.68 to 1,016.5 ± 260.22 counts/100 mL in the dry season and from 641.5 ± 153.44 to 1,275 ± 388.09 counts/100 mL in the wet season, as presented in Table 4 and Figure 21. According to WHO and Ethiopian guidelines, freshwater intended for human consumption should have zero total and fecal coliform colonies per 100 mL to mitigate health risks. However, our bacteriological analysis revealed that TC and FC levels exceeded these permissible limits, indicating high contamination levels in the river water during both seasons. These findings align with earlier studies by Timotewos & Reddythota (2020) and Teklemariam & Wenclawiak (2004), which reported similar TC levels. Based on the Chan et al. (2021) bacteriological risk classification, this study was categorized as high risk for human health. Contamination may stem from excessive suspended materials in the catchment, as well as human and animal waste, which provides a rich organic substrate for bacteria. Thus, from a biological water quality perspective, river water is unsafe for human consumption in the absence of proper treatment.

Figure 21

Mean values fecal and TCs along with sampling sites.

Water pollution status across the Kulfo River sampling sites: The WQI effectively summarizes the overall water quality and identifies key pollutant sources impacting rivers and their tributaries. It aids in selecting appropriate treatment methods to address specific water quality issues and serves as a valuable tool for informing stakeholders and policymakers regarding water resource conditions. The selection of sampling sites in the river was based on water quality. According to the CCME WQI results, sampling site 1 was the least contaminated compared with sites 2 and 3, as illustrated in Table 6 and Figure 22.

Table 6

Calculated CCME WQI values at three sampling sites in the Kulfo River

	Sampling sites
	SP1		SP2		SP3
Factors	Dry	Wet	Dry	Wet	Dry	Wet
No. of failed variables	5	5	6	5	7	5
Total no. of variables	13	13	13	13	13	13
No. of failed tests	10	10	12	10	14	10
Total no. of tests	26	26	26	26	26	26
Sum of excursion_i	−3.44	−1.6	−3.56	−7.23	−8.29	−7.41
Nse	−0.13	−0.06	−1.4	−0.28	−0.006	−0.29
F₁	38.46	38.46	46.15	38.46	53.85	38.46
F₂	38.46	38.46	46.15	38.46	53.85	38.46
F₃	−14.77	− 6.55	−15.84	−38.53	−0.65	−39.87
CCME WQI value	67.46	68.37	61.22	61.51	56.03	61.06
Ranks	Fair	Fair	Marginal	Marginal	Marginal	Marginal

	Sampling sites
	SP1		SP2		SP3
Factors	Dry	Wet	Dry	Wet	Dry	Wet
No. of failed variables	5	5	6	5	7	5
Total no. of variables	13	13	13	13	13	13
No. of failed tests	10	10	12	10	14	10
Total no. of tests	26	26	26	26	26	26
Sum of excursion_i	−3.44	−1.6	−3.56	−7.23	−8.29	−7.41
Nse	−0.13	−0.06	−1.4	−0.28	−0.006	−0.29
F₁	38.46	38.46	46.15	38.46	53.85	38.46
F₂	38.46	38.46	46.15	38.46	53.85	38.46
F₃	−14.77	− 6.55	−15.84	−38.53	−0.65	−39.87
CCME WQI value	67.46	68.37	61.22	61.51	56.03	61.06
Ranks	Fair	Fair	Marginal	Marginal	Marginal	Marginal

Figure 22

CCME WQI value.

The WQI, based on the 13 most common drinking water quality parameters, revealed that the river water samples had the lowest WQI value (56.03 at sampling site 3 during the dry season) and the highest value (68.37 at sampling site 1 in the wet season). Consequently, sampling site 1 was categorized as having fair water quality, whereas sampling sites 2 and 3 fell under marginal quality status. Therefore, sampling site 1 was deemed more suitable for water supply, although significant treatments, including sedimentation, filtration, and disinfection, were necessary.

CONCLUSIONS AND RECOMMENDATIONS

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Conclusions

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Water quality analysis revealed that most of the physicochemical parameters fell within the WHO and Ethiopian safe limits for freshwater drinking water. However, some of the parameters, such as turbidity, solids, organic matter (BOD₅ and COD), and biological indicators (TC and FC), failed to meet the required standards for drinking in both the dry and wet seasons of the sampling period. This indicates that river water requires effective treatment, such as sedimentation and filtration, followed by chlorination, for human consumption. The CCME WQI categorized sampling site one as ‘fair’ for domestic use, while sites two and three were classified as ‘marginal,’ indicating that with appropriate extensive treatment, the water quality at Sites 2 and 3 could meet the required standards for domestic use. However, the significant levels of contamination, including high turbidity and excessive levels of FC and TC, would necessitate substantial and costly treatment processes. Therefore, while technically feasible, it may not be a practical or sustainable solution compared to utilizing Site 1, which requires relatively less treatment. Likewise, pollutant concentrations increased from upstream to downstream due to human activities, such as bathing, washing clothes, and agricultural runoff from fertilizers, manure, pesticides, and herbicides. This study's water quality data and WQI can inform river management plans aimed at improving the overall river water quality.

Recommendations

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Conduct further long-term water quality studies to achieve a more accurate representation of river conditions.
Utilizing CCME WQI results to assist water managers in monitoring and addressing pollutant sources, proposing management solutions, and ultimately reducing water-related health risks.

ACKNOWLEDGEMENTS

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First, we thank GOD Almighty for the guidance and opportunity to achieve our goals in this research. We extend our sincere gratitude to the reviewers and editors for their valuable time, insightful comments, and constructive feedback. Their thoughtful suggestions have significantly contributed to enhancing the clarity, quality, and overall impact of this manuscript. We extend our heartfelt gratitude to our families for their unwavering love and support throughout our journey. We also want to express our appreciation to Mr Benti Chanyalew for sharing his expertise and helping with water quality laboratory sampling analysis. His encouragement is invaluable. Additionally, we acknowledge the residents of Arba Minch for their help with data and sample collection as well as the Arba Minch Town Water Supply and Sewerage Service Enterprise for their support.

FUNDING

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This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.

DATA AVAILABILITY STATEMENT

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

CONFLICT OF INTEREST

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The authors declare there is no conflict.

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