Preheat oven to 350°F (180°C).
Whisk egg yolks, water, salt and pepper until blended; set aside.
Beat egg whites in medium bowl until stiff but not dry. Fold yolk mixture gently into whites.
Spray 8-inch (20 cm) ovenproof skillet with cooking spray. Heat skillet over medium-high heat. Pour egg mixture into skillet, smooth surface lightly. Lower heat to medium-low and cook until omelette is puffed on top and lightly browned on bottom, about 5 minutes.
Place skillet in preheated 350°F (180°C) oven until knife inserted in centre comes out clean, 8 to 10 minutes.
Without cutting all the way through omelette, run knife through top surface slightly off-centre, fill one-half of omelette if desired, then fold omelette in half. Serve immediately.