I use water from my 135F hot water faucet - run first for a bit to get up to temp. Boiling shortens the life of the cups, so by having 2 in cycle and after 6-8 uses each, they last longer.
If I understand correctly, the purpose of boiling is to kill anything growing in the biofilm that protects the mycobacteria, and that film takes some time to form. If, however, I have another infection like pseudomonas going on, I boil after use - then I keep about 4 cups "in cycle" so I only have to do every 2 days.