Melt the butter in a soup pot over medium heat and cook the onions and carrot, stirring occasionally, until the onions soften, about 5 to 8 minutes. Do not let the onions or carrots brown. Sprinkle a teaspoon of salt over the carrots and onions as they cook.
Add the stock and water and the ginger the strips of orange zest. Bring to a simmer, cover, and cook until the carrots soften, about 20 minutes.
Remove the strips of orange zest and discard. Working in small batches, pour the soup into a blender and purée until completely smooth. Only fill the blender bowl a third full with the hot liquid and keep one hand pressing down on the cap of the blender to keep it from popping off. Add more salt to taste. (You will need more salt if you are using homemade unsalted stock or unsalted butter.)