The general cost optimization problem of water distribution networks (WDNs) is categorized as NLP-Hard problem due to the nonlinearity and requirement of discrete pipe sizes. Obtaining the global optimal solution of NLP-Hard problem is always a challenging task. In most of the available techniques, multiple solutions are obtained and the best one is adopted. Hence, the global optimality of the adopted solution is not guaranteed. It is observed that improved solutions of few benchmark problems were provided from time to time by different researchers. This paper aims at suggesting some indicators to check the global optimality of the final adopted solution. These indicators are based on the characteristics observed in global optimal solution by different researchers. The methodology is useful to check the global optimality of solution for a new network. Herein, the methodology is tested with a benchmark network solved by more than 15 researchers, and its improved solution from the previous best is obtained in five occasions. Limitations of the proposed methodology are also discussed.