Day 1: mix the water and flour together until well combined. Cover with tea towel using rubber band and set aside on counter at room temperature
Day 2: remove half of the mixture, and add two tablespoons of flour and two tablespoons of water and mix well. Cover with tea towel and set aside on counter at room temperature.
Day 3-7: repeat process from day two. By day seven it should be active and ready for baking. If not, it may take a few more days of repeating the process. When it is bubbly and smells sour it is ready for baking!
Notes
Maintenance: If you keep it on the counter at room temperature, it needs to be fed every single day. Keep it stored in the refrigerator if you don't plan on baking with it every day. Plan ahead and remove it from the refrigerator and feed it one day before you plan on baking with it.