*2.2. Database Search*

The search through the Scopus and Engineering Village databases was undertaken on the 14th of October 2021 and returned with 1428 and 1316 articles, respectively. However, the Engineering Village database was a combination of three databases: (1) Compendex, (2) GEOBASE, and (3) Inspec. For this reason, many of the 1316 articles were duplicated in the search output. Fortunately, the search engine had a feature to remove these duplications, and the number was subsequently reduced to 721 articles. This result, plus that from Scopus (i.e., 2149 articles) were merged in EndNote Library, which also has the advantage of automatically removing duplications, reducing the total number to 1627 articles. Among these papers, 174 were conference papers, while the remaining were peer-reviewed articles.

Before starting the manual search, inclusion and exclusion criteria needed to be assigned and followed generally. Under these criteria, any articles unrelated to the main scope (i.e., both WRM and sustainability), whether directly or indirectly, would be excluded right away. For example, many articles related mainly to the medical, education, and energy sectors were removed. In addition, if this criterion were applicable, another specific check was required to ensure that these studies had considered a framework or index by mentioning that clearly in either the title or the keywords. Consequently, both conditions were applied in the first screening stage by checking each title and all keywords of the 1627 papers. This stage resulted in a reduction in the number of articles to 400.

In the second round, abstracts were investigated concerning the target group and main elements of the subject domain (i.e., indicator, indicator-based, and component). The results dropped to 45. This round was supposed to be the last round, but after checking some articles among the 45, it appeared they lacked an applicable framework or index that included specific indicators. Therefore, a final round was added to skim-read each of the 45 papers and ensure that they contained these essential elements to be included in the full-text review. Consequently, 23 studies were selected to be included in the analysis. All these screening stages were summarized and illustrated below in Figure 1.

At the end of the systematic review, key methodological steps were applied to help meet underlying objectives, namely:


**Figure 1.** The selection process for articles.
