Our building is still colonized with Legionella.

Thank you very much for your reply. It has been very helpful. However, on meeting with the water treatment company yesterday, he has now advised us that our samples after a year returned a reading of nearly 6000 cfu/mL, and not 825 cfu/mL as we had originally stated. If we chlorinate more regularly we could keep the level to below 1000, cfu/mL, but this would also rot the pipes. Does this new reading alter the advice that you very kindly offered in your previous email?


Chlorination is ineffective long-term against Legionella. Note that there is no clear-cut need to disinfect your  mansion. Keep in mind in your neighborhood all large buildings and 10% of homes are colonized  with Legionella. None of them are undergoing disinfection, nor should they. If you must disinfect, copper-silver ionization is effective but maintenance is necessary.