I am a Senior Director of Engineering for retirement communities. We had a problem in the first two buildings there. Scaling had built up on the copper pipes as the water softening system was not put into operations until 6 months after opening. We suspected that the scaling encouraged the harboring of Legionella bacteria.
1) Is it a reasonable assumption that scaling on pipe assists the bacteria in harboring and subsequently colonizing?
2) As galvanized pipe naturally encourages scale build-up, is galvanized pipe a poor selection for domestic water systems?
3) Does the size of the pipe make a difference?
1) Scale does provide a surface area for bioflim accumulation, but it is not neccessarily a critical factor. We have demonstrated rapid colonization of a newly constructed building. (Legionnaires’ disease in a newly constructed long-term care facility. J. Am. Geriatric Society. 48:1589-1592, 2000)
2) We believe that galvanized pope is not the best choice for water distribution systems. Once of our never facilities was constructed with extensive use of galvanized pop in both the cold and hot water systems. They are now having to replace large sections of pipe due to corrosion. New copper piping is inhibitory to Legionella. We learned this since our early model water systems were constructed of copper; it was difficult to keep Legionella alive in this system.
3) We do not think pipe size is a factor, but we have never tested this hypothesis. We have found that higher flow causes more Legionella to be deposited on the pipe surface due to mass transfer.