In a small saucepan, combine the water and sugar and bring to a boil. Cook over moderate heat, stirring just until the sugar dissolves. Let cool.
Fill a cocktail shaker with ice and add 1/4 cup of the syrup, 1/4 cup lemon juice, 1/4 cup Cointreau and 1/2 cup brandy. Shake vigorously until quite cold and strain into 4 frozen, sugar-rimmed martini glass. Repeat with the remaining ingredients to make 4 more drinks.