Comparative analysis of weighted arithmetic and CCME Water Quality Index estimation methods, accuracy and representation

This paper aims to investigate and evaluate the difference in the computed WQI using the weighted arithmetic method (WAM) and Canadian Council of Ministers of the Environment (CCME) and the reasons of the exaggeration and permissive of these WQIs. In addition, it also aims to specify the suitable WQI computation method in Iraq. Al-Shula City, Baghdad, Iraq was considered as the case study. The results of estimating the WQI in the Al-Shula City using WA and (CCME) methods for each month fluctuated between 0.103 to 8645 and 8.53 to 58.56, respectively. Hence the WQ fluctuated between excellent to unsuitable for drinking (excellent to poor). However, the range of the computed accumulated WA and CCME WQI was between 8 to 3886 and 9 to 59. Consequently, for the two methods, the class of WQ is fluctuated between excellent to unsuitable and excellent to poor. In addition, the calculated CCME WQIs were always lower than the computed WA WQIs. Therefore, the CCME method is permissive or somewhat lenient in contrast to the WA method. Consequently, the WA WQI is more sensitive to presence of toxic contaminants than the CCME WQI. Therefore, the WA WQI is more suitable to use in Iraq because of the high fluctuation in the level and types of pollution sources.