Sterilize a jar by boiling it in a water for 10 minutes then let it air dry on a clean towel
Put water, sugar, honey (if using), and salt in a saucepan over medium heat. Cook until the sugar dissolves. The mixture should be clear and no longer cloudy. Turn off the heat. If you want it thicker, you can cook it over low heat for a bit longer. Keep in mind that it will thicken further as it cools down so you don't want to cook it for too long
Transfer the syrup to the jar and add osmanthus flower. Stir it a bit to combine with the syrup. Let it cools down and then close the lid and let it sits in the fridge for 2-3 days or longer. The longer it sits, the more intense the flavor will be
The syrup can be kept in the fridge for about 2 weeks or longer