Jeremy Laurance: Rest assured - it's safe to leave that bottle of water at home

Medical Life
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There was an engaging spat last week between an outfit called the Natural Hydration Council (sponsors: Danone, Brecon Carreg, Highland Spring and other makers of bottled waters) and the British Medical Journal (sponsor: independently minded docs who don't like being pushed around by conglomerates), which had had the temerity to publish an attack on our current fetish with drinking. Water, that is.

Remember that Smack the Pony sketch in which the camera pans slowly across three women sitting at their office desks? The first has a glass of water beside her keyboard, the second is shown glugging from a litre bottle while the third is pouring the entire contents of a two-gallon dispenser over her head.

It made me laugh then and I was reminded of it again last week when Margaret McCartney, Glasgow GP and newspaper columnist, launched a missile in the direction of Danone and co, alleging they were "pushing" water without good evidence of its benefits.

The advice put out by the NHS, and ably promoted by Danone and the rest, is that we should be drinking between 1.5 and 2 litres of water or other fluids a day to maintain "healthy hydration". "Healthy hydration" is a relatively new concept and its grip on the public imagination is impressive. It is evident in the ubiquity of plastic water bottles in every shop and cafe and the reluctance of even hardened commuters to leave home without one.

But how much water do we actually need? The answer is: it depends. If you are living on a diet that mainly consists of sausages, cake and chocolate you will need more water than if you are eating quantities of fruit, for the blindingly obvious reason that fruit contains a lot of water.

A friend who recently completed a 106-mile cycle ride across Dartmoor wrote to tell me that his cycling partner, a diabetic, drank 7 litres of water and ate five Mars bars and a host of other sugary stuff during the ride, while he downed less than a litre of water and a couple of homemade flap jacks. From which I conclude, as did he, that we are all different.

There are undoubtedly problems with hydration in certain groups – the elderly in particular. Uncles and aunts I have cared for over the years have, to a man and woman, rejected water as a revolting drink, recalling the chlorinated fluid that came out of the taps in their youth, and have all preferred tea, coffee or squash.

We are, of course, lucky to have the choice. Most of the world's peoples do not. But when judging the state of my own hydration I rely on the advice a junior doctor gave me decades ago as I handed him a urine sample for a routine medical test.

"That's too dark – it should be straw-coloured," he said. And that has been my touchstone ever since.