The hot water cylinder for the house is just a bog standard resistive element electric hot water service. The date on the manufacture plate was 2006. Nine years old. Not quite old enough to replace but worth checking the sacrificial anode.
They are made from a metal alloy with a more “active” voltage (more negative reduction potential / more positive electrochemical potential) than the metal of the structure. The difference in potential between the two metals means that the galvanic anode corrodes, so that the anode material is consumed in preference to the structure.
The loss (or sacrifice) of the anode material gives rise to the alternative name of sacrificial anode.
So for $75 from Reece and a 26mm socket I replaced the anode in 5 minutes. The old one was not totally corrode but close. The new one should mean a few more years out of the HWS.
Now it is outside but under the cover of a pergola. With a little bit of time and using leftover pieces of plywood and some corrugated colorbond a hot water box was created.
This was put around the HWS after insulating the tank with some left over thermastop roof blanket. The pipes were insulated with pipe lagging and the whole job means that the HWS is better insulated and hot water should take longer to cool down thus saving money on the power bill.