Preheat your oven to 350°F (175°C) and grease a 9-inch square baking dish.
In a mixing bowl, whisk together the flour, 0.5 cup sugar, and baking powder. Stir in milk and melted margarine until you have a batter; transfer it to the prepared baking dish.
Scatter blackberries over the batter, then sprinkle on the remaining 0.5 cup sugar for topping. Pour in water.
Bake for 45 minutes to an hour or until the batter rises and the top is golden brown.
Let it cool for about an hour before diving in.
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