In a large pot over medium heat, melt butter. Cook garlic in butter 30 seconds, then stir in nutmeg, pepper and salt and cook 30 seconds more. Pour in the water and introduce the cauliflower. Bring to a boil, then reduce heat, cover and simmer 20 minutes, until cauliflower is tender.
In a small saucepan over medium heat, cook carrot with water to cover until just tender. Drain and reserve.
Puree cauliflower soup in a blender or food processor or with an immersion blender. Stir in reserved carrots, green onion and parsley. Serve.