Water nucleophilic attack (WNA) pathway is studied in recent years because of its increasing trend as a promising operative mechanism among Ru based water oxidation catalysts. Taking reference to this, complete WNA mechanism is investigated in order to understand full picture of metal catalysis in water oxidation. A key concern in this part of the study is to be able to have insight why two structurally similar mononuclear catalysts prefer different path (i.e. either WNA or I2M) for O-O bond formation in the catalytic cycle, and secondly, why Ru-bda has better catalytic activity than Ru-tpc. Ground state geometry optimizations were performed by DFT calculations and implicit solvent model (IEFPCM) were employed. Spin density analysis were conducted in order to understand the effect of electronic spin factors on water oxidation mechanism that Ru-tpc and Ru-bda are going to favor (either WNA or I2M) after reaching highly oxidized oxo species.