Engineers | Legionella.org

I work for an education board. We are refurbishing two toilet
blocks (six sinks in each) and have discovered that the toilets are
supplied off a large galvanized water tank in the roof space. The
tank seems well sized and has a good through-put of water, with
feed and supply to the tank on opposite ends. Does an old
galvanised water tank hold any inherent dangers of
Legionella?

Legionella can colonize or contaminate any water tank,
including new tanks. The location of the tank (on the roof) could
result in heat gain during warmer months. So despite having a cold
water supply (low Legionella risk) the tank could acheive
a temperature conducive to Legionella growth.

Galvanized pipes/tanks will result in higher iron in the water.
Higher iron has been associated with a greater probability for
Legionella.

The situation where you should be concerned about
Legionella is in buildings housing individuals at risk for
Legionnaires’ disease (nursing homes, hospitals, etc.).
Legionella may not be a risk in your situation, but you
should test the water for Legionella to provide evidence
for future steps.

There are claims that Legionella can survive at a
chlorine level of 5 ppm at pH 7.0-7.5 in tap water. What is your
opinion of this?

There are multiple reasons for the relative resistance of
Legionella to chlorine. These include an outer membrane
with ubiquinones and other fatty acids, intracellular location
within cysts of amoebae, and genetic responses to oxidative stress
from exposure to chlorine.