## 2 Literature Review  
WQIs that are based on physico-chemical and biological parameters are used for monitoring the quality of water at different locations, such as the United Kingdom [10], Dalmatia [11], Zimbabwe [12], Argentina [13] and India [14]. Over the years, a number of water quality indices have been proposed that first convert raw parameter concentrations into a sub-index or quality rating (q) value and aggregate these indices to obtain a final water quality index value [15]. This value lies in the range of 0 to 100 and is classified accordingly [16]. Among the most commonly used WQIs are NSFWQI, CCME, OWQI, weighted arithmetic WQI (WAWQI) and minimum operator index (MOI) [17]. The classification and number of parameters used for these indices are given in Table 1. WAWQI and NSFWQI use the unit weight (w) and \(q\) of the nth parameter to calculate the final WQI value as seen in Table 1. The CCME is based on: (1) scope \(F_{1}\), (2) frequency \(F_{2}\) and (3) amplitude \(F_{3}\). Some of these indices use expert opinions in identifying important parameters, weight assignment and transformation to sub-indices [10]. Other development techniques include fuzzy interference [19] and the Delphi method is used in NSFWQI, OWQI and the index of water quality (IWQ) [20]. However, the common attribute amongst these indices is the use of physico-chemical variables. Of parameters used, 6% are biological, 24% are physical, and 70% are chemical [21]. Amongst them, the DO, total coliforms have an 87% selection rate [22]. Biological oxygen demand and pH are selected at a 73% rate [23]. Temperature, Tur, ammonia and TDS have a 47% selection rate [24]. The problem identified for most of these indices is that they are very sensitive to the parameters involved in \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Index** & **No. of** **Parameters** & **WQI Value** & **Rating Class** & **Equation** & **Reference** \\ \hline \multirow{4}{*}{WAWQI} & \multirow{4}{*}{10} & 0 to 25 & Excellent & \(n\) = the number of parameters, \\  & & 25 to 50 & Good & \(q_{n}\) = quality rating of the \(n\)th parameter, \\  & & 51 to 75 & Fair & \(\bar{u}_{n}\) = unit weight of the \(n\)th parameter \\  & & 76 to 100 & Poor & \\  & & 101 to 150 & Very Poor & \\  & & Above 150 & Unfit for Drinking & \\ \hline \multirow{4}{*}{NSFWQI} & \multirow{4}{*}{9} & 90 to 100 & Excellent & \(n\) = the number of parameters, \\  & & 70 to 90 & Good & \(q_{n}\) = quality rating of the \(n\)th parameter, \\  & & 50 to 70 & Medium & \(\bar{u}_{n}\) = unit weight of the \(n\)th parameter \\  & & 25 to 50 & Bad & \\  & & 0 to 25 & Very Bad & \\ \hline \multirow{4}{*}{CCME} & \multirow{4}{*}{47} & 95.0 to 100.0 & Excellent & \(F_{1}\) = No. of failed/ Total variables \(\times\) 100 \\  & & 80.0 to 94.9 & Good & \(F_{2}\) = No. of failed/ Total tests \(\times\) 100 \\  & & 65.0 to 79.9 & Fair & \(F_{3}\) = amount by which objectives not met \\  & & 45.0 to 64.9 & Marginal & \\  & & 0.0 to 44.9 & Poor & \\ \hline \multirow{4}{*}{OWQI} & \multirow{4}{*}{8} & \multirow{4}{*}{to 100} & Excellent & \(n\) = number of parameters, \\  & & 85 to 89 & Good & \(S_{I}\) = \(S\)I is the sub-index for the \(i\)th parameter \\  & & 80 to 84 & Fair & \\  & & 60 to 79 & Poor & \\  & & less than 60 & Very Poor & \\ \hline \multirow{4}{*}{MOI} & \multirow{4}{*}{8} & 80 to 100 & Eminently suitable for all uses & \(n\) = number of parameters, \\  & & 60 to 79 & Suitable for all uses & \\  & & 40 to 59 & Main use may be compromised & \\  & & 20 to 109 & Unsusuicide for several uses & \\  & & 0 to 19 & Totally unsuitable for many uses & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Classification of WQI values for five Indices. classifying a water body. Even a single parameter with a slightly high concentration value can affect the index classification [9].