Groundwater is a key source of drinking water in Jordan. This study was conducted to assess the suitability of groundwater in major groundwater basins in Jordan for drinking purposes. The groundwater quality data from sixteen sampling stations within one-year-monitoring period from March 2015 to February 2016 were used. Weighted arithmetic water quality index (WQI) with respect to the Jordanian standards for drinking water was used for quality assessment. Sixteen Physical, chemical and microbiological parameters were selected to calculate WQI. The result showed that all physical and chemical parameters were almost below the maximum allowable level based on the Jordanian standards for drinking. On the other hand, the microbiological parameter (i.e. E.coli count) was exceeded the maximum allowable limit in all the studied locations based on the Jordanian standards for drinking water. The computed WQI values range from 40 to 4295. Therefore, out of 16 studied locations, three locations are classified in the “Excellent water” class, nine locations as a “Good water” class, one as a “Poor water” class, two as a “Very poor water” class, and one as a “Water unsuitable for drinking purpose” class. Furthermore, Escherichia coli is considered the most effective parameter on the determination of WQI in this study. This result highlighted the importance of including the microbiological parameters in any drinking water assessment, since they reflect with other physical and chemical parameters the actual condition of water quality for different purposes.