Preheat the oven to 180 degrees C. Lightly gress a 20cmx30cm baking tray.
In a large bowl stir together the flour, sugar, cocoa powder, baking powder and salt. Pour in water, vegetable oil and vanilla; mix until well blended. Spread evenly in baking tray.
Bake for 25 to 30 minutes in the preheated oven until the top is no longer shiny. Let cool for at least 10 minutes before cutting into squares.