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Diriba and Fitamo

Table 3, were determined based on previous studies by Table 4. The WHO standards 33,34 for drinking
Berhe, Sanad et al., Al-Aizari et al., Panneerselvam water quality, assigned wi, and calculated Wi for
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et al., and Ha et al. 32 each parameter
19,
In the second step, the relative weight (Wᵢ) (Table 4) Parameters WQS Wi Wi
for each parameter is calculated using Equation I, as TDS 1000 5 0.114
described by Panneerselvam et al. 19
pH 7 4 0.091
Wi wi (I) HCO₃⁻ 500 1 0.023
+
n in wi K 2+ 12 2 0.045
3
0.068
Mg
50
Ca 2+ 75 3 0.068
Where W is the relative weight, w is the weight
i
i
of each parameter, and n is the number of parameters TH 500 4 0.091
selected. SO₄²⁻ 250 5 0.114
In the third step, the concentration status (Sc) for each NO₃⁻ 50 5 0.114
parameter was calculated by dividing the concentration PO₄ ⁻ 5 1 0.023
3
of individual chemical variables in each water Cu 2+ 2 2 0.045
sample by the corresponding drinking water quality Total Fe 0.3 4 0.091
standards (WQS) set by the World Health Organization --
(WHO), 33,34 using Equation II, as described by Al-Aizari F 1.5 5 0.114
et al. In the fourth and fifth steps, the overall chemical =44 =1
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quality of the water (Ow) and the GPI were assessed Abbreviations: WHO: World health organization; WQS: Water
using Equations III and IV, respectively, as outlined by quality standards; TDS: Total dissolved solids; TH, Total
Sanad et al. 13 hardness; wi: Weight values; Wi: Relative weight. Note: The pH
value is reported in pH units, while concentrations of all other
parameters are expressed in mg/L.
Sc = C (II)
WQS recommend a maximum nitrate concentration of

where Sc is the concentration status, C is the 50 mg/L in drinking water, the human acceptable value
concentration of individual physicochemical water (HAV) for nitrates is set at 20 mg/L. This threshold,
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quality parameters in each water sample and WQS is the supported by studies conducted by Sanad et al.,
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drinking water quality standard of each physicochemical Al-Aizari et al., and Panneerselvam et al., was used
parameter set by the WHO. 33,34 for calculating the NPI in the present study.
Ow = Wi × Sc (III)
where Ow is the overall chemical quality of the water, NPI Cs HAV (V)
Wi is the relative weight, and Sc is the concentration HAV
status. where NPI is the nitrate pollution index, Cs is the
nitrate concentration in the groundwater (mg/L), and
GPI n in Ow n in WiSc (IV) HAV denotes the human acceptable value for nitrate and
is taken as 20 mg/L. The NPI values for all groundwater
where GPI is the groundwater pollution index, Ow samples were then classified into one of five categories,
is the overall chemical quality of water and n is the as shown in Table 5.
number of parameters selected.
2.5. Determination of WQI
2.4. Determination of NPI The groundwater quality in the study area was assessed
The NPI is a key indicator used to assess the level of using the standard WQI model. This model was
nitrate contamination in groundwater. It plays a crucial selected due to its widely recognized, standardized
role in evaluating water pollution caused by nitrates, approach, which ensures consistent and reliable results
particularly in areas impacted by human activities. across various studies and regions, thereby facilitating
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The NPI was calculated using Equation V, as outlined direct comparisons with other research findings. The
by Sanad et al. Although the WHO guidelines WQI calculation includes thirteen physicochemical
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Volume 22 Issue 1 (2025) 104 doi: 10.36922/AJWEP025040023