A simple formula to get you started
1/2 cup distilled water
1⁄2 cup organic flour (whole wheat or white will work)
Mix the two together, wrap and store at room temp (not cooler than about 65 degrees) for 12 hours.
After 12 hours, add 1⁄4 cup distilled water and another 1⁄2 cup flour, mix in, wrap and store.
The next day, (12 hours later):
Add 1⁄4 cup distilled water and 1⁄2 cup flour to existing starter, wrap and let rest for a full 24 hours.
At this point check your starter – it should be bubbling (if it is not, you will need to discard and start again). If it is bubbling, repeat the adding of 1⁄4 cup water and 1⁄2 cup flour and let rest again for 12-24 hours.
Discard half the bubbling starter and add 1⁄2 cup water and 1 full cup flour. Wrap and store in refrigerator until you are ready to use – following the feeding/Maintenance schedule below:
Once a week, remove starter from fridge, discard half and add 1⁄2 cup water and 1 full cup flour, wrap and let rest a full week in fridge before feeding again.