Reason you don't need to boil distilled is there are no nutrients for the bacteria to feed on. I'd even go as far as saying you're adding impurities to the water by boiling it first (your kettle or pot is not sterilized and the water will go get ions from whatever source it can when pure). Hence adding feed for bacteria. Best way is to open the distilled bottle just before pouring it into you loop.
Edit: Spelling mistakes...
Edited by Rognin - 1/20/12 at 10:42am