First we must trash a soapy tenet of the green-lifestyle movement: showers do not necessarily use less water than a bath. What? Listen and you will hear the sound of top tip number three, "Take a shower instead of a bath", being hastily scratched from a zillion eco-living books.
A study into UK showering habits conducted by consumer-goods giant Unilever has kicked this eco myth into touch. A patented device attached to the shower heads of 100 households monitored water flow and duration of 2,600 showers over 10 days. Families also kept a shower diary (presumably on waterproof paper). The surprising results show we say that we spend far less time in the shower than we actually do. In fact, a typical British family spends more than a week in the shower every year, at a collective cost of £416 per annum. The average duration of each shower is eight minutes per person (not the five we usually admit to) and uses around 62 litres of hot water. A nation with a daily eight-minute shower habit adds up to one that uses 4.2m litres of hot water per day.
Meanwhile wallowing in a bath – previously frowned upon – uses around 80 litres of water. But the fastest-flowing shower in the study used 80 litres in just four minutes and 42 seconds. And power showers can use up 136 litres of hot water per scrub – the equivalent of almost two baths.
A heavy hot-water habit is not only costly (the power-shower scenario would set a family back £918 a year), it's carbon hooliganism that slips under the radar. We each use 150 litres of water per person per day, equating to 35m tonnes of CO2 a year, mostly from heating water. This is so huge that new-build homes with insulation, efficient boilers and low-flow loos are still let down by hot-water emissions that exceed those for home heating.
I'm guessing your brood will not be up for sharing bath water. You could install a more efficient showerhead, flow regulator or tap aerators, but ultimately it's all about timing. By taking a shower that is just one minute shorter, a family of four could save up to £100 a year.
A Water Pebble (waterpebble.com) will record your usage and give you traffic-light warning signals. Alternatively, try standing outside the door with a claxon, giving your guests a two-minute warning. That should get Christmas Day off to a dynamic start.
If you have an ethical dilemma, send an email to Lucy at lucy.siegle@observer.co.uk or visit guardian.co.uk/profile/lucysiegle to read all her articles in one place
