By definition, distilled water has no impurities. You may buy poorly distilled water but the process is supposed to remove impurities. Now you may have worked in boilers but I lived and worked on nuclear submarines for 25 years. Our reactor water (primary coolant) had to be pure to less than 3 parts per million. We made that right on the boat. Our drinking water was more pure than your boiler water. Same with our battery water. Impurities in reactor water became radioactive which was unsat. Rickover used to drink primary coolant when he was before congress to prove a point. Even water that pure will cause iron and other metals to corrode. That's why we used monel metal in our piping.