Preheat the oven to 400 degrees. In a large, non-reactive pot, combine the water, sugar, cornstarch and lemon juice. Stir to dissolve, then add the fruit. Bring the mixture to a simmer over medium heat and cook for a few minutes to cook the cornstarch. Taste and correct the sugar or lemon juice if necessary. Pour the mixture into a greased full –sized hotel baking pan.