Prepare pastry for single crust pie and following baking directions.
Place one cup of the strawberries and the water in a food processor or blender. Cover and process until smooth. Remove and place mixture in a small saucepan. Bring to a boil. Reduce heat and simmer for 2 minutes.
In a slightly larger saucepan, combine cornstarch and sugar. Add water-berry mixture. Cook and stir over medium heat until bubbly. Cook and stir for 2 more minutes. Remove from heat and stir in enough food coloring (usually a few drops will do) to tint a rich red color if desired. Cool to room temperature.
Fold remaining strawberries into cooled mixture and pour into prepared pastry shell. Cover and chill for three to four hours. If desired, top with thawed whipped topping just before serving.