Roast the hazelnuts in a saucepan slowly, without fat, until golden yellow. Attention! Nuts burn quickly and then turn bitter. So always stir diligently. When the nuts are browned, add the sugar and let it caramelize slightly (not all sugar has to melt), then add the water and cook until the sugar has dissolved, then let it simmer for another 10 minutes.
Then pour the syrup through a sieve so that the nut pieces are filtered out. If you want, you can then let the syrup run through a coffee filter, then it becomes very clear.
Bring the finished, filtered syrup to the boil again briefly and then pour it into tightly fitting bottles while hot and close.