Shower or Bath
Even ignoring these sources of inefficiency, a bath might cost 90p. A shower might cost a third of that and even as low as 10p using a aerating shower head which mixes air and water - air has a low heat capacity so it does not take much energy to heat. Using a shower head like this produces a spray, meaning that a large area can be washed in the same time. With a typical saving of 60p per day per person, a family of four can save £2.40 a day, or £16.80 per week, or £873.60 per year. This is maybe a quarter of a their energy bill.