Wash the rosemary and shake dry. Bring 500 ml water, sugar and rosemary sprigs to the boil in a pot. Let simmer for about 10 minutes, stirring several times, until a syrup is formed. Sort the raspberries and put some aside for garnishing. Wash the lemons hot, grate them dry, grate the peel of 1 lemon and squeeze the juice. Cut the other lemon into slices and set aside for garnishing.
Remove the pot from the heat, add the raspberries, lemon peel and lemon juice and leave to stand for about 10 minutes. Remove the rosemary, briefly puree everything with a hand blender and allow the syrup to cool completely. Pour the syrup through a fine sieve.
Wash the mint, shake dry and pluck the leaves from the stalks. Mix 4 tablespoons of syrup in a carafe with 750 ml mineral water. Add ice cubes, some mint leaves, raspberries and lemon slices and serve immediately.
EXTRA TIP: To preserve the syrup, boil a sealable bottle in boiling water for about 10 minutes. Then place the bottle and the lid (without rubber or silicone coating) in a 100° C hot oven for another 10 minutes. In the meantime, bring the syrup to the boil, pour hot into the bottle and close it immediately. Let it cool down and store in the refrigerator. The syrup will keep for several months.