The typical hot-water tank keeps approximately 65% of the tank at the set temperature; the other 35% will be cooler. Also, some water heaters develop a warm zone at the bottom of the tank(beneath the heating element) where scale and sediment often accumulate, providing a perfect habitat for Legionella.
Because hot water use is constant, temperatures may not vary much in hospital hot-water tanks. If temperatures do vary, consider relocating the supply and return taps, installing a top-to-bottom circulating pump or insulating the underside of the vessel.
Installing thermometers at various locations of the tank (say one at each and a third at the middle) will make regular temperature checking easier.