There are different models to calculate water quality Index. You can use any of them or the classic as you mention.

It seems two different questions and the answers for them are as follows:

1. There are so many ways to drive the weights of the parameters for WQI calculation. A robust PCA analysis is not the only way.

2. Yes, a classical PCA can also provide loading weights of each component.

Robust PCA analysis is not always required, but its a justification for assigning weights to the selected parameters in WQI models. Weight are assigned based on parameter importance, and are calculated using different ways/methods.

thank you all

If there are papers that you think are useful, please share them with us.

greetings to you all