Groundwater quality assessment for drinking by weighted WQIs: a guide based on comprehensive review analysis

Currently, the deterioration of groundwater quality (GWQ) is a major global issue, largely due to a fast-growing population and increased agricultural and industrial activities. It is crucial to assess GWQ using effective methods to mitigate the risk of water contamination. In recent years, there has been a notable focus on using water quality index (WQI) values for measuring GWQ. A key step in creating WQI values is to assign weights to GWQ parameters. Even a slight change in these weights can significantly impact the overall GWQ assessment. Various weighting tools are employed in developing WQIs to reduce bias in weight assignment and improve the GWQ evaluation. A thorough review is essential to understand the characteristics of these indices in the context of GWQ assessment for drinking (GWQAD). The goal of this study is to review several weighted-WQI techniques for GWQAD, providing an evaluation of their attributes. A total of 1662 published documents were collected from the Scopus database covering the past two decades (2004–2024). A total of 344 published articles were filtered, which included seven weighted-WQI techniques. The framework, mathematical formulations, applications, advantages, and drawbacks of those WQIs have been discussed. Most models adhere to similar frameworks, although the specific details of the five critical phases vary considerably. Weighted-WQIs are widely used for GWQAD, but each model has distinct strengths and weaknesses, which create challenges for researchers. Therefore, we suggest that a comparative analysis of WQIs will assist in identifying the most suitable WQI method. This review could act as a reference, paving the way for future research endeavors.