In a plastic or glass container with a pop off plastic lid place 1 cup of whole rye flour, and 2 cups of filtered water. With fresh flour no starter is necessary, but 2 tbsp of kefir whey will help older flour. Mix all together, then place the lid on the container and keep in a warm place for 24 hours.
Next day, throw out or reserve half of the starter. Add ½ cup of flour and 1 cup water, mix, then seal
Repeat the above procedure for two more days, and your starter should be bubbly and foamy, and ready to use.
Alternately, place the first day's reserved starter in a similar container, and add also ½ cup flour, 1 cup water, and stir. On the successive days, the starter may either be halved and the excess discarded, or two containers can be added to without removing any starter. If the starter is nice and bubbly, the extra amount will not cause a problem. You are then free to use the second starter as the base for pizza dough, pancakes, or whatever. The other starter can then be used as normal, or as the basis of a slow fermented sourdough bread