Whisk the eggs and water together very well in a small mixing bowl. Season with salt and pepper and set aside.

Melt half of the butter in a medium-sized skillet (I like nonstick) over medium heat until bubbly. Add the mushrooms and sauté for a few minutes or until softened. Season with salt and pepper and scrape into a small bowl. Wipe out the skillet; no need to wash.

Melt the remaining butter in same skillet over medium heat until bubbly. Pour in the egg mixture and cook over medium heat until bottom is beginning to set. Use a spatula to draw in the edges of the omelet gently to allow the still liquidy portions to flow towards the edges and contact the pan, tilting the pan if necessary to facilitate the process. Sprinkle the reserved mushrooms over half of the omelet (save a little bit if you want to place some on top at the end as in the image) and continue to cook until the omelet has a tiny bit of moisture left to it, but isn’t wet, nor overly dry. Fold one half of omelet over onto the other half, slide onto a plate. You can also roll the omelet by tilting the pan over your serving plate and using your spatula to help it roll over on itself. Garnish with reserved mushrooms, if using, and serve immediately.