Evaluation of drainage water quality for irrigation reuse in Kulfo and Hare irrigation command areas, southern Ethiopia

Water is essential for irrigated agriculture (Shamsur et al. 2017). However, irrigated agriculture productivity and sustainability are dependent not only on an adequate supply of water but also on the quality of irrigation water. Irrigation water quality is critical for crop yield, soil productivity, and environmental protection (Laze et al. 2016). If water from agricultural drainage systems is reused for irrigation, it can have a direct detrimental impact on soil productivity due to soil salinization (Ashour et al. 2021).

Good quality irrigation water is, thus, an important component of sustainable irrigated agriculture. Whereas, salinity, sodicity, and ion toxicity are the major problems of irrigation water as they affect soil quality and crop yield (Zaman et al. 2018). The chemical constituents of irrigation water can affect plant growth directly through toxicity or indirectly by altering the soil property and availability of nutrients (Ayers & Wescot 1985). In arid areas where rainfall does not adequately leach the salts from the soil, an accumulation of salts will occur in the crop root zone (Zaman et al. 2018).

The main sources of irrigation water for irrigated agricultural practices around Arba Minch are Kulfo and Hare Rivers. Hence, the source of irrigation water for the Amibara-irrigated agricultural farm and Arba Minch University research farm is the Kulfo River, whereas the Hare River is the source of irrigation water for the Shara and Chano community-managed small-scale irrigated agricultural practices. According to the Ethiopian climate classification, the irrigation command areas of Kulfo and Hare rivers are characterized by hot, semi-arid, warm temperatures, and tropical climates (Haji et al. 2021). The irrigation command areas of the Kulifo and Hare irrigation schemes (Amibara, Arbaminch University Research farm, Shara and Chano community-managed small-scale irrigation farms) are among the large irrigated agricultural areas in the Abaya-Chamo Lakes basin. These four irrigation command areas use surface irrigation systems and surface drainage systems. The command areas dispose the drainage water to Hare River, Abaya Lake, and Kulfo River. The drainage effluent is also reused for irrigation when there is the shortage of canal water. However, it is practiced without proper investigation of the drainage water quality for its suitability for irrigation.

To evaluate the water quality for irrigation, ‘water quality indices’ (WQIs) are employed. WQI is a unitless value distilled from a complex mathematical manipulation based on various hydrochemical properties (Pesce & Wunderlin 2000). Based on primary water quality parameters, WQIs such as Sodium Adsorption Ratio (SAR), Sodium Percentage (Na%), Sodium Carbonate Residual (RSC), Residual Alkalinity (RA), Kelly's Ratio (KR) or Kelly's Index (KI), Permeability Index (PI), Magnesium Hazard (MH), Total Dissolved Ions (TDI), Magnesium Adsorption Ratio (MAR), and Total Hardness (TH) are well-established and used frequently. Therefore, the primary aim of this research was to determine the suitability of water quality of surface drainage systems for irrigation reuse in the research area.

The climate of the river catchments varies from the semi-arid at low lands of rift valley floor to humid high lands of mountain ranges. The annual mean rainfall in the lowlands is 880 mm and the annual mean rainfall in the highlands is as high as 1,541 mm. Two-season annual rainfall pattern prevails in the study area (March to May and September to November). The mean maximum and minimum annual temperatures in the study area are 34.9 and 30.2 °C, respectively.

The river catchments are covered by Tertiary and Quaternary volcanic rocks. The oldest volcanic rocks (Oligocene to Middle Miocene) are found in the study area. The volcanic rocks are distributed considerably in the highlands and slightly on the rift floor (Corti et al. 2013). These volcanic rocks are composed of interstratified ignimbrite beds and basaltic lava flows that have been covered in enormous rhyolites, tuffs, and basalts (Ebinger et al. 1993). The dissolution of silicate minerals in the presence of CO₂ resulted in the release of Na⁺, K⁺, Mg²⁺, Ca²⁺, and HCO₃⁻ to the groundwater and the composition of groundwater is directly related to water–rock interactions in the area. In the research area, therefore, groundwater types are predominantly Ca–Mg–HCO₃ types (Haji et al. 2021).

Samples of surface drainage water and irrigation water were collected from the four irrigation command areas (Amibira farm, Arbaminch University research farm, Shara and Chano community-managed irrigated farms) during the main rainy season (March to May).

The physical and chemical parameters were analyzed for each sample and used to evaluate drainage water for irrigation reuse based on the international standards of irrigation water quality. The water quality for irrigation was assessed using WQIs. The procedure followed is summarized in the following steps:

• Step 1: Designing a water quality monitoring program that covers the investigated command areas (for both surface drainage channels and irrigation canals) for the considered study period.

• Step 2: Collecting water samples from drainage channels and irrigation canals during the main rainy season as surface drainage water occurs in command areas only due to unexpected rainfalls after irrigation applications and the in situ measurement of some water quality parameters.

• Step 3: Laboratory analysis of physical and chemical water quality parameters (for drainage and irrigation water).

• Step 4: Computing the irrigation water quality indices (IWQIs) for water samples (both drainage and irrigation) using standard formulae.

• Step 5: Assessing IWQIs for water quality status and suitability for irrigation.

The recorded and analyzed parameters were (1) three physical parameters: water temperature, turbidity, and total dissolved solids (TDS); (2) fourteen chemical parameters: pH, EC, TH, DO, NO₃, PO₄, and major cation ions Na⁺, Ca²⁺, K⁺, Mg²⁺, and major anion ions HCO₃⁻, CO₃²⁻, Cl⁻, and SO₄²⁻. Temperature, turbidity, TDS, PH, EC and DO were analyzed in the field using Aqua meter and the remaining parameters were analysed in laboratory. This was critical to prepare the parameters for the water quality index irrigation laboratory assessment (FAO 1994).

The physicochemical properties of samples were examined using standard analytical procedures. Sulfate concentrations in water samples were determined gravimetrically using a BaCl₂ solution, whereas Cl⁻ concentrations were determined by titration with AgNO₃. The titration method was also used to determine carbonates and bicarbonates. The extractable cation concentrations (Na⁺ and K⁺) were determined using flame photometry (an instrument with the model: PHF 80B Biology Spectrophotometer was used), whereas Ca²⁺ and Mg²⁺ concentrations were determined using an atomic absorption spectrometer (an instrument with model no. 2380 was used).

Furthermore, 15 mL of 1% ammonium pyrrolidine dithiocarbamate and 30 mL of methyl isobutyl ketone were added to each sample. For 15 min, the mixture was vigorously shaken. Following phase separation, the aqueous layer was drawn off into a clean separating funnel and another 30 mL of MIBK was added, while the upper MIBK layer containing the extracted elements was collected in a small 100 mL separating funnel. The same procedure was repeated three times. The extracted 15 mL aqueous layer of 2N HNO₃ containing the chelated metal from the sample solution was kept in tight-stopper scintillating vials for storage until analysis (El-Amier et al. 2021).

Irrigation water quality assessment is essential to prevent the accumulation of salt or the development of alkalinity or acidity and their effects on the soil moisture movement and its extraction by plants from the soil. To measure water quality, the water quality parameters were calculated using the equations shown in Table 1. The suitability of the agricultural drainage water quality for irrigation purposes was evaluated by the IWQIs such as EC, TDS, SAR, Na%, PI, RSC, MAR, KI, PS, and TH.

Table 1

Drainage water reuse suitability classification based on irrigation water quality factors and their equation

Irrigation water quality factors .	Equations .	Values range .	Water quality suitability category .	Reference .
Electrical conductivity (EC) (μS cm−1)	Aqua meters reading	<250	Low	Adimalla & Venkatayogi (2018)
		250–750	Medium
		750–2,000	High
		2,000–3,000	Very high
Total dissolved solids (TDS) (mg l−1)	Aqua meters reading	<175	Excellent	Chen et al. (2019)
		175–525	Good
		525–1,400	Permissible
		1,400–2,100	Doubtful
		>2,100	Unsuitable
Sodium adsorption ratio (SAR)		<10	Excellent	Richards (1954)
		10–18	Good
		19–26	Fair poor
		>26	Unsuitable
Sodium percentage (Na%)		<20%	Excellent	Wilcox (1955)
		20–40%	Good
		40–60%	Permissible
		60–80%	Doubtful
		>80%	Unsuitable
Permeability index (PI)		>75%	Suitable	Doneen (1964)
		25–75%	Moderate
		<25%	Unsuitable
Residual sodium carbonate (RSC)		<1.25	Good	Richards (1954) and Adimalla & Venkatayogi (2018)
		1.25–2.50	Medium
		>2.50	Unsuitable
Magnesium adsorption ratio (MAR)		<50%	Suitable	Ravikumar et al. (2011)
		>50%	Unsuitable
Kelly's index (KI)		<1	Suitable	Kelly (1940)
		>1	Unsuitable
Potential salinity (PS)		<3.0	Excellent to good	Doneen (1964) and Ravikumar et al. (2011)
		3.0–5.0	Good to injurious
		>5.0	Injurious to unsatisfactory
Total hardness (TH)		0-60	Soft	Durfor & Becker (1962)
		61–120	Moderate
		121–180	Hard
		>181	Very
Irrigation water quality index (IWQI)		0–25	Excellent	Sener et al. (2017)
		26–50	Good
		51–75	Poor
		76–100	Very poor
		>100	Unsuitable

Irrigation water quality factors .	Equations .	Values range .	Water quality suitability category .	Reference .
Electrical conductivity (EC) (μS cm−1)	Aqua meters reading	<250	Low	Adimalla & Venkatayogi (2018)
		250–750	Medium
		750–2,000	High
		2,000–3,000	Very high
Total dissolved solids (TDS) (mg l−1)	Aqua meters reading	<175	Excellent	Chen et al. (2019)
		175–525	Good
		525–1,400	Permissible
		1,400–2,100	Doubtful
		>2,100	Unsuitable
Sodium adsorption ratio (SAR)		<10	Excellent	Richards (1954)
		10–18	Good
		19–26	Fair poor
		>26	Unsuitable
Sodium percentage (Na%)		<20%	Excellent	Wilcox (1955)
		20–40%	Good
		40–60%	Permissible
		60–80%	Doubtful
		>80%	Unsuitable
Permeability index (PI)		>75%	Suitable	Doneen (1964)
		25–75%	Moderate
		<25%	Unsuitable
Residual sodium carbonate (RSC)		<1.25	Good	Richards (1954) and Adimalla & Venkatayogi (2018)
		1.25–2.50	Medium
		>2.50	Unsuitable
Magnesium adsorption ratio (MAR)		<50%	Suitable	Ravikumar et al. (2011)
		>50%	Unsuitable
Kelly's index (KI)		<1	Suitable	Kelly (1940)
		>1	Unsuitable
Potential salinity (PS)		<3.0	Excellent to good	Doneen (1964) and Ravikumar et al. (2011)
		3.0–5.0	Good to injurious
		>5.0	Injurious to unsatisfactory
Total hardness (TH)		0-60	Soft	Durfor & Becker (1962)
		61–120	Moderate
		121–180	Hard
		>181	Very
Irrigation water quality index (IWQI)		0–25	Excellent	Sener et al. (2017)
		26–50	Good
		51–75	Poor
		76–100	Very poor
		>100	Unsuitable

All ions are expressed in meq l⁻¹.

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In the research area, the suitability of the agricultural drainage water quality for irrigation purposes was categorized using the descriptions of different authors (Table 2): The suitability category was evaluated based on IWQI factors, such as EC, TDS, SAR, Na%, PI, RSC, MAR, KI, PS, and TH, and water quality index of irrigation (WQII).

The results of the analysis of physiochemical characteristics of forty-five surface drainage water samples, collected from the drainage channels for four irrigation command areas during the period of the main crop sowing season in 2022, are presented below. The physical and chemical parameters of the drainage water were compared with the international water quality standard for irrigation.

The water samples contained varying amounts of constituents of physical and chemical properties, which are of prime importance in evaluating the quality of water for irrigation (Table 2). The chemical composition of irrigation water is presented in Table 3.

The average EC of surface drainage water in the study area has the minimum value of 352.49 μS cm⁻¹ at the Shara drainage system and the maximum value of the EC of 685.79 μS cm⁻¹ at the Amibara drainage system (Table 2). The value of EC for irrigation water was 173.72 and 232.30 μS cm⁻¹ for the Kulfo River and the Hare River, respectively. Therefore, according to Adimalla & Venkatayogi (2018), the drainage water quality falls under the ‘medium’ salinity of drainage water quality classification. Irrigation water sources quality classification stands at ‘low’ salinity of irrigation water (Table 3).

The PI for irrigation water quality systems takes into account the soil's Na⁺, Ca²⁺, Mg²⁺, and HCO₃⁻ concentrations (Doneen 1964). The drainage water quality demonstrates that the minimum PI value was 25.93% and the maximum value of PI was 42.65% at the drainage channels. The PI value for irrigation water from the Kulfo River was 35.02% and the Hare River was 35.42%. Therefore, based on PI values, all samples of irrigation water sources in this study area were highly suitable and the drainage water was considered to be acceptable for irrigation purposes (Table 4).

When sodium and soil interact with each other, the permeability of the soil will be reduced. Sodium concentration in the surface water is expressed in percent, which is also used to identify Na hazards. The Na% of the surface water in the study area has the minimum value of 20.81% at the head of the drainage canal system and the maximum value of Na% was 34.74% at the tail of the drainage canal system (Table 4). The value of Na% is 27.88 and 27.94% for the Kulfo and Hare Rivers, respectively, as sources of irrigation water. Therefore, according to Wilcox (1955), all drainage water samples are good or safe for irrigation (Table 5).

The SAR of water in the study area has the minimum value of 1.75% at the head of the drainage water system and its maximum value is 2.98% at the head of the drainage water system (Table 4). As a source of irrigation water, the value of SAR is 3.78 and 3.11% for the Kulfo and Hare Rivers water, respectively. Therefore, according to Richards (1954), the sampling sites of the four irrigation command areas fall under ‘excellent’ (Tables 4 and 5).

The Na⁺, Ca²⁺, and Mg²⁺ concentration levels in the water are used to calculate the value of KI as an essential measure in the evaluation of irrigation water quality (Kelly 1940). In this study, the KI of the drainage water in the study area has the minimum value of 0.21 and the maximum value of 0.53 at the head of the drainage water system (Table 4). The value of KI for the Kulfo River and the Harie River is 0.38. As a result, the sampling sites for the command areas have a Kelly value of less than 1 and are classified as ‘suitable’ (Tables 4 and 5).

A high level of MAR (>50%) in a water sample causes soil alkalinity. In this study, the MAR of the water in the study area has the minimum value of 7.28% and the maximum value of 17.81% at the head of the drainage water systems (Table 4). The values of MAR for the Kulfo and Hare Rivers are 10.56 and 10.11%, respectively. Therefore, in the irrigation command areas, all water samples are categorized as less than 50% and this indicates it is suitable for irrigation (Tables 4 and 5).

PS is another water quality parameter-based index for classifying irrigation water (Doneen 1964). In this study, the minimum value of PS of the water in the study area is 4.04 and the maximum value is 4.67 at the head of the drainage water system (Table 4). The values of PS in the Kulfo River and the Hare River are 3.96 and 3.58, respectively. Therefore, according to irrigation water quality standards, the irrigation command areas' drainage and irrigation water samples are classified as ‘good’ to ‘injurious’ (Tables 4 and 5).

Water with high NaCO₃ concentrations is more likely to precipitate Ca²⁺ and Mg²⁺ in the soil. Irrigation is typically deemed safe when RSC levels are less than 1.25 meq l⁻¹. In this study, all water samples are good or safe for irrigation (Tables 4 and 5) because all samples fall under less than 1.25 meq l⁻¹ RSC (Tables 4 and 5).

Total hardness is the sum of calcium and magnesium ion concentrations. The maximum value of drainage water TH in the study area is 27.35 at the head of the drainage water (Table 4). The value of TH in irrigation water is 21.99 and 19.78 for the Kulfo and Hare Rivers, respectively. All water samples collected in the irrigation command areas are classified as soft water (Table 5).

The suitability of the drainage water for irrigation reuse was evaluated using the following IWQI factors: EC, TDS, SAR, NA%, PI, RSC, MAR, KI, PS, and TH (Tables 4 and 5).

In this study, the minimum IWQI value in four irrigation command areas is 47.84 in the Harie River irrigation water and the maximum is 84.89 in the Amibara irrigation water (Table 6). Water samples from the drainage water system indicated very poor in the Amibara irrigation command area; poor in the Chano community irrigated farm, and Arba Minch University research farm. Water samples from the drainage system of the Shara community irrigated farm, Kulfo River (KR) and Hare River (HR) are categorized under ‘good suitability’ (Table 7). Therefore, the drainage water of the irrigation command areas, except the Shara community-irrigated farm, needs treatment before reuse for irrigation purposes.

The primary effect of high EC irrigation water on crop productivity is the inability of the plant to compete with ions in the soil solution for water (physiological drought). In this study, the minimum value of 352.49 μScm⁻¹ of EC was recorded at the Shara community-managed small-scale irrigation command area. Whereas the maximum EC value of 685.79 μS cm⁻¹ was recorded at the Amibara irrigation command area. Therefore, the present findings showed that drainage water quality for irrigation purposes with respect to EC was medium to highly suitable categories across all the sampling locations. This study corroborates the findings of Adimalla & Venkatayogi (2018) who reported that the EC level groundwater in a semi-arid area was not exceeding the normal range. Furthermore, this finding was also supported by different researchers (El-Amier et al. 2021).

TDS are a major factor affecting water quality for irrigated agriculture and depend upon minerals and ions such as Ca²⁺, Mg²⁺, Na⁺, K⁺, CO₃⁻, HCO₃⁻, Cl⁻, SO₄²⁻, and PO₄³⁻. Water used for irrigation can vary greatly in quality depending on the type and quantity of dissolved salts. In the present study, the minimum value of TDS was found at the Shara community-managed small-scale irrigation command area to be 96.64.34 mg l⁻¹. Whereas the maximum value of 542.65 mg l⁻¹ was found at the Chano community-managed small-scale irrigation command area. Therefore, the result indicates that the category of drainage water quality for irrigation reuse was good to excellent. The water containing TDS less than 525 mg l⁻¹ is considered to be in the range of good to excellent water quality category for irrigation. Giri et al. (2022) also used TDS to evaluate water quality for irrigation. They reported the extent of salinity hazards could be measured by the ability of water to conduct an electric current since conductance is a strong function of the TDS measurement. Several scholars supported these research procedures (Chen et al. 2019).

The PI irrigation water quality system takes into account the soil's Na⁺, Ca²⁺, Mg²⁺, and HCO₃⁻ concentrations (Doneen 1964). In the present study, the PI value of all the locations of the drainage water system ranged from 25.93 to 42.65% and the PI value of irrigation water from the Hare River was 35.02% and it was 35.42% of the Kulfo River water. These findings indicate that both drainage and river water samples fall into the moderately suitable category for irrigation. The study concluded that there might be slightly higher Na⁺, Ca²⁺, Mg²⁺, and HCO₃⁻ at those sites (Doneen 1964). The procedure of the study is also supported by similar studies by Giri et al. (2022) and Singh et al. (2020) who reported that irrigation water quality in terms of PI level was moderately suitable when the value was 25–33%.

The Na⁺, Ca²⁺, and Mg²⁺ levels in the water are used to calculate the value of KI as an essential measure in the evaluation of irrigation water quality (Kelly 1940). In this study, the KI of the drainage water in the study area has the minimum value of 0.26 and the maximum value of 0.53 at the head of the drainage channel. As a result, it indicates that for all samples, Kelly's value was <1 and is classified as ‘suitable’ for irrigation. This might be due to the dominant levels of Ca²⁺ and Mg²⁺ in all the water samples (Kelly 1940; Alharbi 2018; Giri et al. 2022) and they report that the water is suitable based on the KI result of 0.74–0.94.

When sodium and soil interact with each other, the permeability of the soil will be reduced. The sodium concentration in water is expressed in percent, which is also used to identify Na hazards. The Na% of the surface drainage water in the study area has a range value of 20.81–34.74% at the head of the drainage channels. From the head of the irrigation canal (before applied in the command area), the Na% value is 27.88 and 27.94% for the Kulfo and Hare Rivers, respectively, as sources of irrigation water. Therefore, according to the results, all drainage water quality samples were good or safe (Wilcox 1955). This might be due to the lower abundance of Na⁺ in all the water samples. This result supports the findings of the irrigation water quality standard by Giri et al. (2022) and Wilcox (1955) who found that the standard of irrigation water ranges from 1.28 to 2.01 and the water is suitable.

The SAR is also related to the Na% in the irrigation water, with a slight difference. The higher level of Na⁺ replaces the Ca²⁺ and Mg²⁺ and the quantity of Na⁺ that is getting adsorbed to the soil is called SAR. A higher SAR would cause a higher reduction in water permeability (Haritash et al. 2016). The SAR value of drainage water in the study area ranges from 1.75 to 2.98%. The value of SAR was 3.78 and 3.11% for the Kulfo and Harie Rivers, respectively. Therefore, according to the results, all sample sites of the command areas fall under ‘excellent’ quality for irrigation (Richards 1954). Giri et al. (2022) used SAR levels to categorize water suitability for irrigation and their study supports this by using and following a similar way in this study.

Mg²⁺ is the crucial element that determines water quality for irrigation. Ca²⁺ and Mg²⁺ maintain the cationic equilibrium, but higher Mg²⁺ alters the agricultural yield after releasing Na⁺ from the soil (Ayers & Wescot 1985). In this study, the maximum average MAR level of the drainage water in the study area was 16.66% and the minimum MAR level was 7.28% at the head of the drainage channels. The values of MAR for the Kulfo and Harie Rivers were 10.11 and 10.59%, respectively. Therefore, the surface drainage and irrigation water quality of the command areas are less than 50%, which indicates they are suitable for irrigation. This might be due to the low level of Mg²⁺ in all the collected water samples. The studies reported by Giri et al. (2022) and Ayers & Wescot (1985) used MAR level to categorize the source of their irrigation water as not suitable for irrigation purposes.

PS is a Cl⁻- and SO₄²⁻-based water quality index for categorizing irrigation water (Doneen 1964). In this study, the PS value of drainage water ranged from 4.04 to 4.87. The PS values of Kulfo and Hare Rivers water are 3.96 and 3.58, respectively. Therefore, according to irrigation water quality standards based on PS, in all irrigation command areas, the surface drainage water and irrigation water samples are classified as ‘good’ to ‘injurious’. This could be due to the slightly lower Cl⁻ and SO₄²⁻ levels in all the water samples. The procedure followed is supported by the studies of Giri et al. (2022), El-Amier et al. (2021), and Doneen (1964). The lower Cl⁻ and SO₄²⁻ levels indicate water is suitable for irrigation, whereas water with a PS value of >5 indicates not suitable for irrigation purposes.

The comparative study of Ca²⁺, Mg²⁺ as HCO₃⁻ and CO₃⁻ is described as RSC. A higher level of Ca²⁺ and Mg²⁺ deposition as HCO₃⁻ and CO₃⁻ will increase the Na⁺ level in the soil. Furthermore, an excess amount of CO₃⁻ and HCO₃⁻ to Ca²⁺ and Mg²⁺ may influence the quality of the water for irrigation purposes. The surplus amounts of CO₃⁻ and HCO₃⁻ will mostly interact with Ca²⁺ than Mg²⁺ and this will cause precipitation. Therefore, this will cause the inverse ion exchange process, which ultimately causes sodium hazards (Haritash et al. 2016; Singh et al. 2020). In this study, all samples are good or safe for irrigation, because they all fall under less than 1.25 meq l⁻¹ RSC's. This study was similar to the study by Singh et al. (2020), where they used RSC levels to categorize good quality water for irrigation purposes.

Assessment of drainage water quality is required to reuse it for irrigation purposes without compromising the soil quality and crop production. The quality of agricultural land drainage water depends on the quality of irrigation water, the chemical and physical properties of soils of the agricultural land, and chemical inputs used for crop production and soil amendments. The suitability of drainage water for irrigation reuse can be evaluated by analyzing the IWQI factors of water samples from drainage effluents. Therefore, in the current study, 19 water sampling sites (4 on irrigation canals and 15 on drainage channels) were strategically selected in four irrigation command areas. The studies conducted on the water samples collected from sampling sites in three rounds with 10-day intervals during the main rainy season showed the following findings.

The study on the water samples from the irrigation canals indicated that the two rivers are safe and permissible with respect to alkalinity and have low salinity and hardness. Moreover, the IWQI factors indicate that the Kulfo and Hare Rivers are good to excellent quality for irrigation.

The results of the analysis of the water samples from surface drainage systems indicated that the drainage water of the Amibara irrigation command area is very poor in terms of IWQI, whereas the drainage water quality of the Chano community-managed small-scale irrigation farm and Arba Minch University research farm are categorized to be poor for irrigation reuse. But the IWQI of water samples from drainage systems of the Shara community-managed small-scale irrigation command area was found to be good for irrigation reuse. Therefore, the surface drainage effluent of the Amibara irrigation command area, Arba Minch University research farm, and Chano community-managed small-scale irrigation command area need treatment before reuse for irrigation purposes.

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

The authors declare that there is no conflict of interest.