Water quality index (WQI) is used for aggregate assessment of water pollution level. The method is used in the United States of America (USA) and some other countries including Vietnam, but it has several limitations: the weight of a parameter is subjectively defined by the experts' criteria; the hierarchical rating scale is self‐regulated and fixed; the individual index of WQI is calculated based on the segmented linear function, which are not convenient to apply in reality when expanding to an arbitrary number of selected survey parameters. In addition, in some cases, WQI results in ambiguity and eclipse (collectively called ‘Virtual effect’). To overcome these disadvantages, the author proposes Relative Water Quality Index (ReWQI). ReWQI's calculation is simple and it does not encounter ‘Virtual effect’. Results of ReWQI have been compared with results of the traditional method used by Department of Natural Resources and Environment of Hai Duong in 2016–2018.

中文翻译：

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相对水质指数（ReWQI）–总体水质评估的新方法

水质指数（WQI）用于水污染水平的综合评估。该方法在美国（美国）和包括越南在内的其他一些国家/地区中使用，但是它有一些局限性：参数的权重由专家标准主观定义；等级评定量表是自我调节和固定的；WQI的个体指数是基于分段线性函数计算的，在扩展到任意数量的所选测量参数时，实际不方便应用。此外，在某些情况下，WQI会导致歧义和日蚀（统称为“虚拟效果”）。为了克服这些缺点，作者提出了相对水质指数（ReWQI）。ReWQI的计算很简单，并且不会遇到“虚拟效果”。