Can my home’s water heater harbor Legionella?

My roommate was just diagnosed with Legionnaires’ disease. About 10 days ago, our hot water heater had to be replaced. Our landlord typically buys them secondhand. Could the not-so-new water heater be the source of the bacteria?


My roommate is on Humira and Methotrexate to treat rheumatoid arthritis so his immune system is compromised. Many thanks for your time!

The information that you have provided is insufficient to answer your question. It is theoretically possible that your roommate could have contracted Legionnaires’ disease from you home water supply, but the hot water heater is not necessarily the cause. Legionella was likely in the drinking water prior to installation of the heater.

See the article Coming of the 3rd Plague

You can ask your health department to culture your home water supply for Legionella. If they cannot or will not do it, it is possible that we could assist. Before we can do that, we need confirmation from your roommate’s physician that the diagnosis of Legionnaires’ disease is absolutely correct and we need to see the actual lab test result. In the meantime, your roommate should not drink tap water.


FYI – We recommend that transplant patients and highly immuno-suppressed patients do not drink tap water. Instead, boil water and cool it for drinking. When traveling or not at home, bottled water might be preferred.