Deseed the cherries (reserve some for garnish) and crush the stones in a mortar. Then stir the pulp through a sieve and leave the juice together with the crushed seeds in the refrigerator for 1 hour to allow the flavors to fully develop. Then add the mineral water and strain the juice. Stir in the sugar and store the juice in the refrigerator until use. Before serving, stir in the maraschino and serve the cherry cocktail with ice cubes and a cherry.