Do you recall that pithy quote a while ago from Ken Livingstone? No, not the one about Fleet Street journalism being a “squalid and irresponsible little profession”, though, Lord knows, that still cuts deep. I mean the one where he urged Londoners to conserve water by saying: “If it’s yellow, let it mellow, if it’s brown, flush it down.” Actually, no, he didn’t. That was me being a squalid journalist. What he said was: “There’s no earthly reason why someone should flush the toilet when they have urinated.”

Well, make that this week’s motto because for a change we’re not going to talk about saving money, but saving the planet. To get in the swing I’m writing this with greasy hair while wearing yesterday’s knickers. Hygiene, you see, is the first casualty when you accept the “20-Litre Challenge”.

Thirsty Planet, a charity bottled water company, sent me a plastic container with a tap on it, the idea being that I go for 24 hours using only 20 litres of water for everything – drinking, washing, flushing, hamster-dunking. (Oh, that’s a joke. I’ve become very fond of my hamster, so enough hate mail, thanks.) This amount of water would serve a villager in rural Africa, but for us it’s two flushes of the khazi.

I know I sometimes sound flip, but water-waste genuinely riles me. In restaurant toilets I’ll stomp like a nutter after women who have left the tap running, saying: “Excuse me, I think you forgot something.”

As you’d expect, it’s a nightmare for the spoilt Westerner to exist on 20 litres a day. Whenever our water goes off for an hour I practically have a breakdown, screeching: “This is ridiculous.” But it’s scary how quickly a finite amount whittles away, after teeth-brushing, tea-making and washing your hands.

Yet I must challenge a couple of Thirsty Planet’s tips. For a start: “Showers use less water than baths.” Not if teenagers are in the house. I’ve yet to meet one who doesn’t spend 40 minutes minimum beneath a shower. And “Only flush when absolutely necessary” is pretty subjective. I mean, fine, if it’s your child’s fairy wee, but if your husband has been out sinking a pint or six, I’d say it’s fairly vital to flush the frothy results. Two friends who have long adhered to Ken’s advice cheerfully admit that their bathroom “hums”. And stagnant urine causes furring, so you have to use industrial-strength bleach, which isn’t terrific for the planet either.

I’m all for ditching washing machines, not overfilling kettles and chucking dishwater over the plants, but, please, stink-free toilets are the key to civilisation (unless you live in France). We work the longest hours in Europe and have crippling mortgages – can’t we at least have the consolation prize of a pristine bog?

bargainhunter@thetimes.co.uk

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