Cutting & pasting from Falkinham paper some salient points about showering:

NTM infection can be a consequence of inhalation of an NTM aerosol (shower) or swallowing water with NTM and the NTM aspirated as a consequence of gastric reflux.

(1) Raise Water Heater Temperature. Turn up your water heater to 130° F (55° C). NTM patient household plumbing that did not have NTM had higher hot water temperatures (130° F or 55° C or higher), compared to households whose hot water heater temperature was 125° F (50° C) or lower (Falkinham, 2011).

(8) Replace Showerhead with One that Produces Fat Streams and Not a Mist. NTM cells are concentrated in aerosol droplets (Parker et al., 1983). Many “low-flow” showerheads produce a fine mist that contains droplets with high numbers of NTM; small enough to enter the alveoli. Replace such a “low flow” or misting showerhead with one that has large holes (greater than 1 mm diameter).