Mix the sugar and the orange peel. Pour 500 ml of water over it and bring to the boil while stirring. As soon as the sugar has dissolved, simmer on low heat for 10-12 minutes. Remove from heat and let the syrup cool down.
Then pass through a sieve, squeezing out the orange peel well. Cover and refrigerate. (The syrup will last for several weeks).
Mix the orange syrup and juice in a large jug. Add ice cubes as desired, fill up with mineral water, garnish with orange slices and serve immediately.