Am I drinking enough water?

Let’s check the science: Should I be drinking water frequently to make sure I’m not dehydrated?

My wife tells me I don’t drink enough water. She says I’ll end up with kidney disease. I see lots of people who carry around a bottle of water and constantly take sips from it. Apparently they believe that they need to “stay ahead” of dehydration, making sure their bodies are fully hydrated at all times. Should I join them?

The promoters’ arguments – science or red flags?

This extract from a web page (here) typifies some of the advice that you can find on the web:

To operate efficiently, the body requires at least eight glasses of water per day, or around two litres. Even more water is needed during hot weather, periods of illness, and when exercising. Many people don’t get this amount of water, choosing instead to get their intake of liquid through coffee, tea, soft drinks, juice and so forth. The problem with this is that many of these drinks have a diuretic effect – forcing the body to eliminate more water than is actually entering it, causing dehydration.

It is vital to note that the two most common signs of dehydration – a dry mouth or feeling thirsty – are not actually the first signs. Once these symptoms occur you are already dehydrated.

But other places, such as here,  have different advice:

You don’t need eight glasses of water per day.
No scientific evidence supports the “eight glasses per day” rule, so you can simply drink in response to thirst. You can also monitor the volume of your urine. If your urine is scanty, dark, and smelly, you should drink more. If you have not urinated during your work or school day (8 a.m. to 3 p.m.), you are severely under-hydrated.

Do I detect any red flags? Neither of these sites gives references to published studies, so they are expecting me to take their word on authority. And quite a few ‘hydration’ websites are run by corporations that market bottled water (here, here and here) or sports drinks (here), so there’s the possibility of conflict of interest and confirmation bias.

Being skeptical

It’s always seemed to me that we have a perfectly good sense of thirst which tells us to drink when we need to, so I find it hard to accept that I need to force myself to drink when I don’t feel like it. Our ancestors managed to survive in conditions where they didn’t have constant access to water precisely because they evolved good hydration-control mechanisms. It’s also pretty obvious that our bodies take in water from food as well as everything we drink, and it doesn’t matter how we get the water, all of it is equally available to our body tissues.

I’m suspicious that companies selling drinks are behind the push for us to drink more fluids. Sellers of bottled water would want us to drink more plain water, whereas the makers of rehydration drinks would try to convince us that they are more efficient than water.

So I’m interested in finding out how much I need to drink under normal conditions, whether I need to drink pro-actively and if so, what’s the best way of doing it.

The scientific evidence

This is one of those situations where there’s an overwhelming amount of information on the web, with lots of publications from seemingly reputable sources. Although it’s even been tackled by Snopes.com, I decided to press on with my own investigation. Eventually I decided I had to limit myself to papers published in peer-reviewed journals or other sources I felt I could trust. Many of the papers were from the British Medical Journal (BMJ).

Here’s an outline of what I discovered:

1. Much of the hype around hydration comes from the bottled water and sports drink industry (here, here and here).
2. Coffee, tea, and soft drinks are just as good as pure water in contributing to hydration (here and here). Of course, water is preferable, but for other reasons.
3. Healthy humans are able to regulate their body water balance with remarkable precision (here and here).
4. Thirst is the best indicator of the need to drink. There is no need to drink pro-actively to ‘stay ahead’ of thirst (here, here, here, here and here).
5. The commonly held view that we must drink 8 glasses of water a day has no scientific support (here and here).
6. Urine colour is not recommended as an indicator of dehydration (here).
7. There is some evidence that increased water intake can reduce the chances of some kidney diseases, but the situation is not clear (here, here, here and here).
8. Overhydration, from drinking too much water, can be dangerous (here and here). Update 28 Sept 2012: Here’s an ABC news report describing how a bushwalker died after drinking too much water.

Conclusion

As I thought, I don’t need to drink huge quantities of water every day. All I need to do is drink when I’m thirsty. If I’m doing heavy exercise or it’s especially hot I should make sure I don’t put off drinking, but otherwise, I don’t really need to think about it.

I certainly won’t be buying bottled water continually. When I need to drink, I’ll have tap water (or perhaps a coffee). The environmental damage caused by the manufacture, transport and disposal of bottled drinks far outweighs even the exaggerated health claims of the drinks industry, let alone the real science.

Further reading

Bottled water is the marketing trick of the century at The Conversation.

No, You Do Not Have to Drink 8 Glasses of Water a Day by Aaron E. Carroll at The New York Times.

This is one of ScienceOrNot’s Let’s check the science series.