Why are you so obsessed with the cost of energy
I think I am annoyed at being conned for years. I was told so many times it was cheaper to use gas, and I never questioned it. The same when I moved here, was told cheaper to use oil, and again never questioned it. It was not until I had solar panels fitted, and as a result had an off-peak supply, that I even considered heating water with electric, and found it was very much cheaper to oil, clearly if not using solar or off-peak the difference would not be as much, but it seems I have been conned for years.
The cost is mainly due to heating pipes and boilers, before the hot water ever arrives at the tap. And it would depend on how much and how often DHW is used, as to how much it costs. If either the pipes and boiler has not fully cooled before next use, or if we are using a lot of water each time tap is turned on, the percentage loss to water used will decrease. And in the early days my dishwasher and washing machine were hot fill, and we were a family of five, so someone would be washing there hands most of the day, so pipe work never cooled.
Today I wash my hands maybe 6 times a day, so with my wife 12 times a day (going to loo) needing around a litre a time, but running off 4 litres to get the 1 litre of hot water. So looking at an under sink water heater instead. Mother house the gas boiler was next to the sink, but still not instant hot water, it took so long to heat the boiler, still running 4 litres of water to get one warm litre to wash hands.
There are so many variables, to sit back and say gas is x-p/kWh and electric y-p/kWh does not work, Distance boiler or cylinder to taps which have a huge effect, and also distance boiler to cylinder. My boiler (oil) would run for 20 minutes once a day, but old homes the boiler was turning on/off maybe 20 times a day for 3 minutes a time, even when tap very close to the boiler, for taps further away may run 5 minutes. So only real way, is to in summer when no central heating being used, to see how much gas burnt in a day, week, lunar month etc.
Since old homes the gas boiler also used for the shower, there is no way I could have measured how much gas water heating cost compared with electric. So I am asking the question, can anyone actually give some real figures?