The formula
litres = shower + toilet + washing machine + dishwasher + other uses
Where it comes from
Household use across western Europe averages around 130 litres per person per day. The shower is usually the biggest single use in the home: a normal head runs about nine litres a minute, and considerably less with a low-flow one.
How to work it out by hand
- Multiply the minutes in the shower by nine litres and by the number of people
- Add the toilet flushes at six litres each
- Add the washing machine and dishwasher spread across the day
- Add about twenty litres per person for cooking and cleaning
What is worth knowing
Two changes move the bill noticeably: a low-flow shower head drops from nine litres a minute to six without the shower feeling different, and a dual-flush cistern halves the water on every short use. Turning the tap off while brushing your teeth, on the other hand, saves very little in absolute terms, however good a habit it remains.