I was coming home on the train last week, counting water bottles. This isn't my latest perversion, just mild interest at how we've all swallowed the water con. Roughly one in four passengers were lugging bottled water around, including myself. Are we in the middle of a dehydration epidemic? Or are we all just a bit mad?
Let's start with me. I like my wee to be fairly dilute and clear. There's no particular rationale for this, other than it proves I'm not dehydrated and it doesn't smell too bad when you splash it all over the seat and floor and don't have time to wipe it up. Right guys?
I picked up the habit of drinking too much water after advising parents that a good way of spotting whether their children were dehydrated was to see how much they were weeing. Heavy nappies good, dry nappies bad. Full clear stream good, dark yellow trickle bad. The trouble with drinking lots of water is that, surprise surprise, it makes you pee a lot more, so you're up and down like a bride's nightie.
If you're of a nervous disposition, you could equate the increased peeing with a prostate problem (unlikely if the stream is good) or even diabetes.
I've seen patients who've tricked themselves into thinking they were ill when all they were doing was overdoing the water.
The World Health Organisation estimates we need two litres of clean water a day. This is to replace the litre we pee and the litre we lose through sweat and breathing. Tap water is as good for you as bottled, and the water doesn't all have to come in water form.
Most food has lots of water in it (cucumber contains 98 per cent, fruit and fish 80 to 90 per cent and meat 30 per cent). Add in the coffee and beer and you don't need to drink two litres of water on top. If you do, your kidneys will just remove it (along with all the vitamins you're taking that you don't need).
Excess water doesn't harm you, unless you're drowning, but neither does it detoxify you. Some people binge drink cold water to try to reduce their appetite for food but that doesn't seem to work either. Hangovers and hot weather may be excuses to lug a bottle around, but most of us can rely on a brilliant evolutionary mechanism to tell us when we need water: thirst Dr Phil Hammond is a GP, writer and broadcaster