I've always used water from a boiled potato to make my starter. Mix 1:1 this with white flour. Put is a loosely coverd glass jar with room to expand. It will sour within 24 hours. As you use starter, replace with equal parts flour and water. You can refrigerate the starter to slow it down. You should use some or discard some each week and recharge it.
Fantastic! I've tried to be self-sufficient in a lot of things and this is one more. I can't wait to try it.