The water quality index (WQI) is a well-defined tool that replicates the composite influence of individual physico-chemical parameters on overall water quality (Sahu & Sikdar 2008; Gupta
et al. 2016). To estimate the WQI, the assigned weightage (
wi), relative weightage (
Wi) and recommended standards (WHO 2006; Bureau of Indian Standards (BIS) 2012) for drinking water quality parameters such as pH, EC, TDS, TA, TH,
, Cl
−,
,
and Fe for both seasons are represented in Table 2. The assigned weightage on physico-chemical parameters ranges from 1 to 5. Firstly, the relative weight (
Wi) is formulated by the following equation.
where
Wr,
wi, and
n represent the relative weight, weight of each physico-chemical parameter, and the number of parameters, respectively.
Table 2Relative weight of physico-chemical parameters
| Parameters
. | WHO standards (2006)
. | BIS standards (2012)
. | Weight (wi)
. | Relative weight (Wi)
. |
|---|
| Desirable value
. | Permissible value
. |
|---|
| pH | 6.5–8.5 | 6.5–8.5 | NX | 4 | 0.114 |
| EC | 2,000 | 2,000 | NX | 3 | 0.086 |
| TDS | 1,000 | 500 | 2,000 | 5 | 0.143 |
| TA | 200 | 200 | 600 | 2 | 0.057 |
| TH | – | 200 | 600 | 3 | 0.086 |
| Cl− | 250 | 250 | 1,000 | 4 | 0.114 |
 | 200 | 200 | 400 | 4 | 0.114 |
 | 45 | 45 | NX | 5 | 0.143 |
 | 0.3 | – | – | 3 | 0.086 |
| Fe | 0.3 | 0.3 | – | 2 | 0.057 |
| | ∑wi = 35 | ∑Wi = 1 |
| Parameters
. | WHO standards (2006)
. | BIS standards (2012)
. | Weight (wi)
. | Relative weight (Wi)
. |
|---|
| Desirable value
. | Permissible value
. |
|---|
| pH | 6.5–8.5 | 6.5–8.5 | NX | 4 | 0.114 |
| EC | 2,000 | 2,000 | NX | 3 | 0.086 |
| TDS | 1,000 | 500 | 2,000 | 5 | 0.143 |
| TA | 200 | 200 | 600 | 2 | 0.057 |
| TH | – | 200 | 600 | 3 | 0.086 |
| Cl− | 250 | 250 | 1,000 | 4 | 0.114 |
| | 200 | 200 | 400 | 4 | 0.114 |
| | 45 | 45 | NX | 5 | 0.143 |
| | 0.3 | – | – | 3 | 0.086 |
| Fe | 0.3 | 0.3 | – | 2 | 0.057 |
| | ∑wi = 35 | ∑Wi = 1 |
where Wr, wi, and n represent the relative weight, weight of each physico-chemical parameter, and the number of parameters, respectively.