I looked a bit into it and maybe I am not that far off with my explanation if the OPs water heater is a 2-element model: (broken link removed) I doubt it explains a full 46 kWh difference, on the other hand who knows if that is solely the hot water or just the TV left on a bit longer. Given the low electric usage I would look at other places, like offsetting the remaining demand with a PV system or saving on gas for the car(s). Or being really progressive in my lifestyle: http://www.solarcookers.org/