Pour the warm water in a bowl of a stand mixer. Add the yeast and let dissolve, about 5 minutes. Stir.
Add the olive oil and the flax, oat flour and buckwheat flour. Mix with dough hook on Speed #2 until incorporated. Add the carbonated water and start gradually adding the Caputo flour. Once all the flour has been added, mix until all incorporated and smooth.
Meanwhile dissolve the salt in a little warm water. Add the salted water. Mix until smooth and incorporated.
Turn up the speed to high and beat for 5 minutes to incorporate air into the dough.
Cover with plastic wrap and a tea towel. Place in a draft free area for approximately 40 minutes until risen.
Oil 3 loaf pans with olive oil. Divide the dough between the 3 pans. Smooth the tops. Cover with plastic wrap and preheat oven to 425 F. Let dough rest covered 15 minutes.
Place on middle rack and bake until fully cooked, about 20-25 minutes. Check internal temperature with a meat thermometer ...should be between 205-210F
Remove from pans and cool on a wire rack. Freeze well.