I think you misunderstood. I use filtered tap water. And you are correct, the boiling takes care of any problems with it.

As for using boiled water, that is not something I do. But what I have read is use clean, covered glass bottles to store the boiled water, so it stays safe until used. When I can, or put up fresh orange juice, I clean my bottles by washing in hot soapy water, then rinsing with boiling hot water. I believe that meets with the approval of Dr Joe Falkinham, the accepted expert on NTM in water.
Sue