Put flour, baking powder, sugar, nuts and maccha in a bowl and mix together
Add the eggs, vanilla, & water, and mix well until a soft dough forms (this will take a while, as the dough needs to be really worked so that its stays together and has a good feel).
Place the log on a greased baking tray on bake for 30 minutes
Remove from the oven and allow to cool completely.
Slice the log into 8 pieces and place on a lined baking tray. Bake for 10-15 minutes or until the biscotti are crisp