Beat egg yolks in a medium mixing bowl until thick and lemon colored; add water, salt, and pepper, mixing well.
Beat egg whites (at room temperature) in a small mixing bowl until stiff but not dry; fold into yolk mixture.
Heat an ovenproof 10-inch omelet pan or heavy skillet over medium heat until hot enough to sizzle a drop of water. Add butter, rotating pan to coat bottom and sides. Pour in egg mixture, and gently smooth surface. Reduce heat; cook 5 minutes or until puffy and lightly browned on the bottom. Transfer pan to oven; bake, uncovered, at 350° for 7 minutes or until a knife inserted in center comes out clean.
Sprinkle chopped ham over half of omelet. Loosen omelet with spatula, and fold in half. Gently slide omelet onto a warm serving plate. Garnish with parsley. Serve immediately.