Juice the orange into a jar with a lid and add 1 teaspoon of orange zest.
Add the balsamic vinegar, olive oil, water, Dijon mustard, black pepper, and salt. Close it with the lid and shake it until all of the ingredients are fully combined.
Notes
Adjust to taste: Try it and adjust any element to your preferred flavor.
Let it rest: I recommend leaving the orange juice salad dressing for at least an hour to allow the flavors to meld.
Shake/whisk between servings: It will separate while it sits, so make sure to stir or shake it well before serving each time.