Using a cherry pitter or a sewing needle, push out the pits of the cherries over the saucepan or pot you are going to use (so that you don’t lose the juice). Add the water to the pits and set aside for 10’.
Put the sour cherries and sugar in the saucepan. Sprinkle with the water of the pits (without the pits), cover, and refrigerate for about 12-14 hours.
The next day, boil the mixture of cherries over medium heat for about 30’ minutes (until syrup thickens). Stir gently while cooking and skim off any scum that rises to top. Add lemon juice at end of cooking time to prevent the color and also the syrup from crystallizing.
Wait for the sweet to get cold, spoon into sterilized jars, and refrigerate.