Combine the blueberries, 1 cup of the sugar, water and lemon juice in a large saucepan and bring to a boil.
Simmer gently while preparing the topping.
Measure the remaining 1/4 cup sugar, flour, salt and baking powder into a bowl; stir to blend.
Cut in the butter.
Add the milk and stir until moistened.
Drop by spoonfuls over the simmering berry mixture.
Simmer, covered, for at least 15 minutes longer.