Is boiled water safe to use in machines that require distilled water?

Boiled water may contain salt, high levels of minerals, and chlorine. Hard water can damage the efficiency of whatever it is you are using. For example, my daughter's bottle sterilizer over a few months had started to show signs of erosion. We had extremely hard water and were inconsistent with filling our water softner. At the same time, the salt from the water softner was probably equally as damaging. You can boil the water until the cows come home, but minerals and metals do not boil out. Hope that answers your question.