In a large skillet, melt butter over medium-high. Add cabbage and cook, stirring occasionally, until it begins to soften and brown around edges, 4 minutes. Add water, cover, and cook until cabbage is crisp-tender, 5 minutes. Uncover and season with salt and pepper. Add tomatoes and cook, uncovered, until they soften, 3 minutes. Stir in vinegar. Season to taste with salt and pepper and top with parsley.