Humans can survive in the desert, but Death Valley is not the first place I would choose to look for them, especially not if I was looking for a large population.

Can we agree that the higher the temperature, the quicker the kill time for Legionella? Can we agree that metal is a very good conductor of heat? So, when the flame on my gas heater is turned on by the thermostat, doesn’t the bottom of the tank get pretty hot in order to transfer heat to the tank, and heat the water in a reasonable amount of time? Sounds like the bottom of my tank is kinda like Death Valley for Legionella.

Legionella are aerobic. I think it’s an extremely important characteristic that is useful to know, but everyone else is free to think otherwise.

Yes

Also sediment and calcium in the bottom of tanks promotes legionnaires

The higher the setpoint the lower your efficiency

Gas in particular can see significantly higher efficiencies below 130f

Oxygen is only one factor in the growth of aerobic bacteria. Bacteria do need nutrients. Aerobic bacteria grow better on surfaces rather than suspended in a liquid.

A household water system doesn’t appear to be homogeneous to me. Faucets, shower heads, drains are all part of a household water system and they are a quite different environment from a water line. Bacterial growth is far more likely in a sink drain than in a water line.

A pipe with significant flow is quite a different environment from a pipe with little or no flow. A cold water pipe is quite a different environment than a hot water pipe. Pex is different from copper. Plastic is air permeable. Copper is air-tight and anti-bacterial.

A stagnant pipe could facilitate some biofilm growth because flow will not wash it away before a significant amount forms. A stagnant pipe could effectively become a closed system with very low concentrations of oxygen. No effective source of oxygen flowing into the stagnant pipe. A stagnant pipe could end up with some headspace as gases do not stay 100% in solution. Disinfectant concentration will dissipate in a stagnant pipe. Some of these factors encourage bacterial growth and some do not.

A whole house filter could easily have headspace if not purged when the filter is replaced.

Not sure what point your making.
I think the oxygen source to support the bacterial growth we are concerned with is in solution inthe incoming fresh domestic water which is turned over. There is no air space or “head space”.

My point is that knowing that Legionella is aerobic will help inform you how Legionella will grow at different rates in different locations in a system with varying conditions. Conditions for bacterial growth do vary in a household water system.

My wine example is valid. Growth of aerobic bacteria is inhibited by keeping headspace to a minimum. For example, if your whole house filter housing gets air in it, it will be more likely to get contaminated by aerobic bacteria.

Your example closed system was designed specifically to inhibit aerobic bacteria by limiting the presence of oxygen. The system designer must have thought it was important. But, somehow you know it isn’t an important factor in an open system.

Legionella is real and definitely grows in fresh water, so apparently there is enough oxygen in the water to grow the organism. There is no question about the potential danger posed by standing luke warm fresh water.
It’s why we never use fresh water in hydronic heating systems. Hydronic heating systems must be closed loop with no fresh water introduction. Introducing much fresh water, (as in auto make up valves) or using piping materials that are not oxygen tight with encourage gas exchange through the material into the heating water causing corrosion issues, especially with iron and steel system components. Typically the PEX tubing we use in floor heating system is coated with Ethyl Vinyl Alcohol, EVOH, to limit oxygen exchange though otherwise permeable polyethylene.

Dale,

The amount of oxygen in water is far lower than in air. Bacteria tend to live nearer to the surface of water where oxygen is far more plentiful.

As a winemaker, a main part my job is to limit exposure to oxygen. We regularly top our oak wine barrels to limit oxidation and limit the growth of aerobic contamination bacteria, such as acetobacter.

Fresh water is saturated with oxygen.