Wash the pomegranate, cut off the top. Make several deep longitudinal cuts on the peel with a knife. Dip the pomegranate in a wide bowl of water, peel it. Gently release the grains from the inner membranes. Sort the cranberries, rinse and put on paper napkins so that all the water is glass.
Fold the pomegranate seeds and cranberries into a sieve, squeeze the juice with a wooden pestle. Add juice to a container with mineral water, stir and pour into glasses.