Day 1: In a glass jar, mix 1 cup of whole wheat flour with 1 cup of filtered water. Cover with a cloth and secure with a rubber band. Let it sit at room temperature for 24 hours.
Day 2: Discard half of the mixture. Add 1 cup of all-purpose flour and 1 cup of filtered water. Stir well, cover, and let sit for another 24 hours.
Day 3-5: Repeat the process of discarding half and feeding the starter with 1 cup of all-purpose flour and 1 cup of filtered water every 24 hours. By day 5, the starter should be bubbly and have a pleasant sour smell.