No, there is no benefit whatsoever. Which is handy to remember if you happen to be stranded mid-ocean and someone suggests drinking wee.

Mark Smith and Steven Freeman said they survived for 11 days after their yacht capsized recently in the South China Sea by, among other things, drinking their own urine. But experts argue they probably would have been in better shape if they had stayed away from their own waste.

First the technicalities: there's nothing inherently toxic in urine. "If you don't have any urinary infections, urine is aseptic. It doesn't contain any bad bugs," says Toni Steer of the Medical Research Council Human Nutrition Unit in Cambridge. "I've always heard that if you need to sterilise a wound, then urine is quite good."

But urine is no use for keeping you alive. Remember what the stuff is there for: to get rid of the various things in your blood that you cannot store or use relatively quickly. The kidneys are continually purifying the blood of these extraneous chemicals, and the resulting cocktail is dissolved in water and sent merrily out of the body.

"Your body is really good at saying, 'Christ, I haven't got enough water' and hanging on to it for dear life, while getting rid of what it has to get rid of," says Mike Stroud of the Institute of Human Nutrition at Southampton University. "Your urine becomes very concentrated very quickly. If you drink it, in order to get rid of what you're now introducing, even the sodium in the urine will take more water to get rid of it than you have water in the urine. It inevitably dehydrates you."

Dr Stroud says there is just one situation where urine might be useful - if, just as your ship sinks, you happen to be completely drunk. "Like you just had eight pints of lager and you were peeing like crazy," he says. "Arguably, the first couple of urines, if you kept those, might just possibly give you more water than salt."

As for non-emergency situations, Stroud dismisses those who believe urine could be beneficial - for everything from chickenpox to skin and hair problems - as "daft as brushes".