Just found a whole bunch of UK studies of hot water – Yay! Here’s one on the cost-benefit of installing thermostatic mixing valves:
Here’s a powerpoint from the American Burn Association discussing scald prevention:
It looks like Legionnaire’s disease has very low prevalence in the US. I don’t know how much other bacteria is in water tanks, nor the prevalence of disease and death caused by these bacteria, so I’m really not certain how this would affect tank temperature recommendations. My recent conversation with a tech rep at one water heater manufacturer suggests that they are primarily concerned with litigation stemming from scalds, and consequently recommend the very low tank temperature of 120F. It seems unfortunate that manufacturers allow their fear of potential litigation to trump the greater interest of society. Most residential tanks can be set as high as 160F.
It seems likely that the tank should be set fairly hot (>140F?), and outgoing water immediately mixed down to low-scalding potential temperatures (12*?). The murky issue is tank temperature – is the likelihood of bacterial problems sufficient to justify turning the tank temperature up? If so, too what?