Add filtered water and sourdough starter to a large bowl and stir to combine.
Add rye flour and salt to bowl and combine well with a stiff wooden spoon until a wet dough forms- almost like a very thick batter.
Cover the large bowl with a plate or damp tea towel or kitchen towel and let rest for 30 minutes.
After 30 minutes, uncover the bowl and with wet hands, stretch and fold the dough by pulling up the sides and pressing down to the opposite side of the dough ball. Repeat this about 10 times, and form into a round shape.
Place the dough ball in the bottom of the bowl, then cover and let the rye dough rise in a warm/room temperature place for about 6 hours.
After 6 hours or so, the dough will be risen slightly and no longer look like a ball. Use wet hands to form the dough into a ball again, then transfer to an airtight container (or cover a bowl with a damp cloth and a secure plate/lid.)
Place dough in the refrigerator to long ferment for 24-48 hours.
45 minutes prior to baking, preheat oven with a pizza stone or cast iron pizza pan inside to 450 degrees Fahrenheit.
Remove rye dough from the refrigerator and turn dough onto work surface.
Sprinkle flour over dough ball, then press dough down onto parchment paper and form into a 1/2 inch thick (or thinner) pizza round.
Once oven is fully preheated, add desired pizza toppings.
Carefully transfer pizza round on parchment paper to pizza stone
Bake for 8-12 minutes, or until outer crust and cheese (if using) is slightly golden brown.
Enjoy!