There are two commonly suggested temperatures for hot water tank thermostats: 60 °C or 49 °C (140 °F or 120 °F).
For many years (and in some places, presently), 60 °C was the recommended temperature. At 60 °C, the water in the tank is hot enough to kill any bacteria trying to set up shop inside the tank.
However, water at that temperature is also hot enough to cause third-degree burns in seconds. This makes it necessary to install mixing valves, which drop the temperature of the water after it leaves the tank. BC Hydro, for example, currently recommends setting your hot water tank at 60 °C.
If you do, you need to test the temperature of the hot water coming out of each faucet and shower in your home to ensure it’s under 49 °C at that point.
Government of Canada health authorities, meanwhile, suggest setting the tank at 49 °C. This is still hot enough to kill the overwhelming majority of bacteria, but cool enough to avoid scalding anyone in the home. Plus, it uses less energy than setting it at 60 °C.
Though, homes with immunocompromised occupants should set the temperature at 60 °C to be certain no lingering bacteria survive — just make sure you’ve got your mixing valves set up.