Use a rather large mixing bowl-the batter will rise to double its original volume. Put the water in the mixing bowl and sprinkle in the yeast. Let stand to dissolve for 5 minutes. Add the milk, butter, salt, sugar, and flour to the yeast mixture and beat until smooth and blended. (I often use a hand rotary beater to get rid of the lumps.) Cover the bowl with plastic wrap and let stand overnight at room temperature. Just before cooking the waffles, beat in the eggs, add the baking soda, and stir until well mixed. The batter will be very thin. Pour about 1/2 - 3/4 cup batter into a very hot waffle iron. Bake the waffles until they are golden and crisp. This batter will keep well for several days in the refrigerator.