My cpap machine humidifer calls for distilled water but could I just boil water and use it instead?

Ideally no but ok. Distilled water or highly filtered water is recommended for humidifier so as not to get minerals deposited in machine or on reservoir wall. Boiling water does ensure it is clean and free of bacteria which is good. It does also rid some of minerals but it does not distill it, leaving heavy minerals like calcium still left in there. Once in a while probably okay but otherwise, better off w/dist.