Drain the cherries and set aside. Place cherry juice (from can or jar) in a 3 quart saucepot. Add in sugar and heat until gently boiling. Add in water and cornstarch and heat on medium until mixture boils gently and thickens, about 3-5 minutes. Cool well and stir in cherries.
Chill well. Makes about 2 cups.
If you have fresh sour cherries, you could use them (pitted of course) and substitute cherry juice or water for the liquid. Otherwise this uses imported sour cherries that come in a jar.