Hello, I hope I can help with your questions, but you must find a balance for yourself.

First, MAC exists everywhere, indoors, outdoors, in the air, in the soil, and in water. Unless you live in a sterile bubble you will always have some exposure. The art is in finding out how to live your best life while minimizing exposure.

As for when and whether to mask, here is my approach (others may differ)
I mask in crowds, especially indoors. I mask when I garden (actually disturbing soil or releasing dust into the air) and when walking outdoors in windy/dusty conditions. I do not mask in my home, but due to allergies and in an effort to minimize impurities, I use HEPA air filters in my house all the time, changing the filters as recommended.

As for sterilizing water, many people recommend it - I choose not to do it as I have a well and had the water tested (no MAC.) I do drink bottled spring water when not home, per the recommendation of Dr Falkinham, the expert on NTM in water. But I am about minimizing exposure, not completely eliminating it, so I don't worry about ice in my drinks when eating out.

I wash my neb, Aerobika, etc daily in soapy water, and sterilize weekly. This is important especially to avoid introducing any new and unwelcome bacteria or fungus to the lungs.

I'm not sure what you mean about toilets?
Sue