@pfists Shari -- I forgot one other thing the engineer said about shower heads. He does a monthly hot water routine -- turn the tap on as hot as possible and let it run for 10 - 30 minutes (very unscientific!) I know that Mycobacteria is killed by 140 deg. water so maybe it works. Apparently he has not any any reinfection and he claims that doing that does the trick. The Australian speaker also advises letting your taps run at very hot temperatures for about 5 minutes before using for the day -- to clear out overnight stagnation. Even longer if you have not turned on your water for a long time. I'm afraid I'm not too good at remembering to do any of this. Mary