[alvah]

This has always struck me as dumb, as until recently it was far cheaper to use your existing (gas-fired) hot water than to use a resistive element. However, with gas going out of fashion (and already hugely expensive in the Eastern states), and abundant solar PV, the calculus has changed.

[selcuka]

The problem is that the first few litres of the water coming from the hot water pipe may be cold or warm. Therefore adding a resistive element is a better solution to guarantee a specific temperature.

[seanmcdirmid]

Gas (especially just in time) still works well for water heating even if you can use heat pumps for everything else. No sure when that will flip, I assume it will eventually.

[alvah]

Gas is already outlawed for new builds in Victoria, despite vast gas resources in the Bass Strait. Presumably that's the direction other states are heading too.