Melt the butter in a large skillet over medium heat; cook the tomatoes in the melted butter until they begin to fall apart, 5 to 7 minutes. Add the basil, olive oil, garlic salt, salt, and pepper. Slowly stir the flour into the mixture and cook until it begins to thicken, 5 to 7 minutes. Stir the water through the mixture to break up any lumps of the flour. Mix the garlic into the sauce and simmer another 5 minutes. Serve hot.