Urban or rural ?
What tariff are you on and what kind of meter do you have?
There are different kinds of methods by which you can end up paying different prices for electricity. One is if you are metered and charged according to the time of use (TOU), the other is if you have certain loads connected to a special circuit commonly shown on your bill as a "controlled load" (like hot water, slab heating, heatbanks etc)
If your bill has references to PEAK SHOULDER and OFF-PEAK then you are on TOU, and so long as this is where your hot water is connected, you just need to make sure you switch it on at the right time.
There are other more complicated set-ups but usually for larger installations. (I had four meters when I first moved in here (farm), but I had it all changed to time of use metering).