It is very interesting to learn from The Lancet Infectious Disease, June 2003 article that virtually all outbreaks have been linked to potable water, and that showering is not a mode of transmission (except perhaps for high risk patients?).
Showering is allowed even for high-risk patients. Highly-immunosuppressed patients and COPD (emphysema) patients should drink bottled water or boiled water that has been cooled, but this is optional. If the percent of distal water sites is < 30%, we do not prohibit showering or drinking water for most patients even if Legionella is present in the water.