Mix eggs, flour, milk, sugar and salt to make a smooth pancake dough. Let the dough rest for 1 to 2 hours.
Stir in the carbonated water at the last moment, just before cooking the pancakes.
Heat an 8-inch frying pan. When the pan is hot, add ¼teaspoon of the butter. Let the butter melt and cover the bottom of the pan.
Pour a ladle of the batter into the pan, and gently tip and twist the pan so that the batter covers the entire pan. When the top of the batter bubbles, turn the pancake over and cook for 4 or 5 seconds longer. Remove the cooked pancake.
Continue until the batter is all cooked; add butter before cooking each pancake.