Mix flour, 1 1/2 cup water, and sourdough starter together in a large bowl to make batter. Cover loosely with plastic wrap and let sit in a warm place until filled with large holes and bubbles, 4 hours to overnight.
Stir oil, eggs, sugar, and salt into the batter; mix well to combine.
Whisk 1 tablespoon water and baking soda together in a small bowl until dissolved. Fold into the batter with a rubber spatula.
Preheat a waffle iron according to manufacturer’s instructions.
Pour batter onto preheated iron and bake until crisp and golden, according to manufacturer’s instructions, about 3 minutes.