Heat a skillet over medium heat on your stovetop. While the pan warms, whisk together the eggs, water/milk, and sea salt. Melt the butter. When the butter is completely melted, add the whisked eggs. Gently stir the eggs as they cook, using a wooden spoon or a heatproof spatula. When they are nearly done, fold in the spinach and the cheese (if you are using cheese). Cover until the spinach wilts (about 1 minute). Serve immediately!