@ansley I am not an expert on this topic but have learned a lot about NTM/MAC from reading and asking questions.

When I wash lettuce or anything else, I think about water age. So if a tap hasn't been used a while, I make sure to run it until the water is as cold as it gets. Once produce is rinsed I make sure to dry as much as possible. So for lettuce I use a salad spinner, which removes most of the water. If it were I with MAC, I'd focus on careful practices with drinking water, reflux management, cleaning/sterilizing nebulizer equipment daily and listening to your pulmonologist as long as they are on board with the program! It's so easy to go overboard with the precautions once one starts.

Here is a list of reducing exposure tips from the NTMinfo group. Washing produce/lettuce in sterile water is not on the list.
https://ntminfo.org/reducing-exposure/
And I am curious, where did you read it was good to use sterilized water for washing lettuce?