Wash the cherries and remove the stems. Pit the cherries.
Mix the cornstarch with just enough of the water to make a slurry.
Combine the sugar and pectin powder. Place this, together with the remaining water, in a saucepan and bring to a boil. Add the cherries and cook gently until tender, 4 to 5 minutes. Strain, reserving the cherries and the syrup s