Preheat the oven to 175 degrees C. Grease and line an 8 inch square tin with parchment paper and set aside.
Sift together the flour, caster sugar, cocoa powder, baking powder and salt and whisk to combine.
In another bowl, whisk together the water, oil and vanilla.
Add the dry ingredients to the wet ingredients and gently whisk to combine making sure that all the dry ingredients are well mixed in.
Transfer the batter to the prepared tin and bake in the preheated oven for about 20 minutes until the brownie is cooked and a skewer inserted in the center comes out almost clean.
Allow the brownie to cool completely before removing from the tin and cutting.