MAC, Pseudomonas and other bacteria are everywhere and everyone inhales it just as everyone inhales other "things" in the air. If you smell it, you are inhaling it – some good smells like popcorn, chocolate (yum), perfume and some bad like smoke, diesel and garbage. Healthy lungs have great filters but those of us with lung diseases, such as bronchiectasis, get rid of most of the junk, but sometimes can't get rid of all of the bacteria. The bacteria can colonize in the mucus trapped in our blocked airways causing the disease.
As for swimming, I'm not sure how water containing any bacteria gets in the lungs because we don't breathe in the water. I think bacteria, like that flesh eating horror, gets in the body through a wound of some sort. I would check with my doctor before putting any part of my body in water that has not been treated. Even then, I read somewhere that chlorination does not kill MAC. I do go into the pool at my health club to take water aerobics but do not go in the pool if I have a wound.