Combine eggs, water, and salt in a bowl and briskly whisk with a fork just until yolks and whites are thoroughly blended. (One secret to a light, fluffy omelet is not overmixing. If eggs are room temperature, yolks and whites will combine more readily.) Whisk in cubed butter and herbs. The combination complements the flavor of the eggs instead of overpowering it: Unsalted butter adds a creamy richness, while tender herbs add freshness.