Stir in lemon juice and second amount of water. Fill ice cube trays using 2 tbsp per cube. Freeze. To store, remove cubes to plastic bag or container. To serve, use 3 parts water to 1 part cordial or 2 cubes to 3/4 cup water. Stir briefly to combine. Makes 84 cubes.
Place sugar, first amount of water and tartaric acid in saucepan. Heat and stir until sugar dissolves. Remove from heat.