In a small sauté pan, melt 2 tablespoons of the butter until foaming. Over medium heat, sauté the shallots and garlic until the shallots are translucent, 2 to 3 minutes. Stir in the tomato and cook for 1 or 2 minutes longer. Pour in the wine and vinegar, turn up the heat a little and reduce until 1/2 cup remains. Pour in the water and reduce by half. Strain the sauce into a clean pan. Whisk in the remaining 4 tablespoons of butter and season to taste with salt and pepper; keep warm.