Warm the water over medium heat in a saucepan. Stir in the sugar and mineral drops, and continue stirring them into the hot water until the sugar dissolves completely. Remove the sugar water from the heat, and allow it to cool to room temperature.
Place kefir grains into a jar, pour the sugar water over them. Set the Kefirko's strainer on top of its jar, and top with a loose-fitting lid to allow for limited airflow. Allow the water kefir to culture for 24 hours, then remove the lid and strain the water kefir into a pitcher.
Whisk the orange and cranberry juices into the water kefir, then pour evenly into swing-top bottles. Seal the bottles, and allow the kefir to culture for 2-3 days at room temperature, keeping in mind that the cooler your kitchen is, the longer it will take to culture and the warmer your kitchen is the shorter it will take to culture.
Serve right away or transfer to the fridge. Take care when opening the bottles as the fermentation process creates carbon dioxide which may cause the water kefir to fizz and foam.