Ok Tips, I did some research & OSHA was on top of my list last night, including the CDC...
For OSHA: http://www.osha.gov/SLTC/legionnairesdisease/index.html
There are first of all NO OSHA standards
Lets also remember that their definition is: Domestic water systems are designed to provide cold or heated water for washing, cleaning, consumption, etc. The term "domestic" applies to all non-process water used for lavatories, showers, drinking fountains, etc., in commercial, residential, and industrial settings. You have to remember that OSHA writes this stuff for commercial & industrial facilities where you would probably choke on how water is handled as compared to a regular house
Most cases I know of,or heard of, were actually caused via the HVAC and other associated systems - drinking fountains I know where a hot topic for a while also
While they did one report & have all sorts of suggestions for where outbreaks occored & ideas for preventing it, they also recomended running it non stop with a hot water recirculating pump, and chlorinating / using biocides a few times a year - are you selling this to your customers?
With that said, they also point out that - L. pneumophila bacteria are widely distributed in water systems. They tend to grow in biofilms or slime on the surfaces of lakes, rivers and streams, and they are not eradicated by the chlorination used to purify domestic water systems. (Gees, where's the EPA when you need them)
If I was concerned about this, I would probably recomend a UV filter before I would even suggest running water heaters at above 140 degrees,much less going putting a constant recirculating pump in. Oh and of course following the recomended maintenance, etc... Based on the cause and how it spreads, you would quickly see that the issue isn't in the house, but lack of backflow preventers & monitoring of the actual water source - maybe this is another item where we would be better to foccus on the real issue before jumping in saying we are here to kill you with our energy efficiency standards. Just a thought