Place the fruit in an enameled or stainless saucepan and pour water over. Boil over high heat, then reduce to a simmer. simmer for 10-15 mins until tender.
With the back of a spoon rub through a fine sieve set over a mixing bowl and add sugar (i would taste after a 1/2 cup). Return to the pan and bring to a boil again. Reduce heat to moderate, stir in the dissolved potato starch and, stirring constantly cook another 2 or 3 minutes until it thickens slightly. Cool to lukewarm and pour into dessert dishes. Refrigerate at least 4 hours before serving.