I have seen so many peopel that worry needlessly about their hot water. from people who think that a half filled kettle or having a shower insyead of a bath will save the planet, to people who think that solar water heaters on theior rooves will save half their heating costs - when its half their water heating costs.
I use the same ampunt of hot water summer and winter, In summer I use virtually no oil at all. In winter I use over 250l a WEEK