Do we need eight glasses of water a day?

What does the new study say?

There's very little scientific evidence for any of the supposed health benefits of drinking a lot of water. Of course, you should drink when you feel thirsty. As long as you drink enough fluids to keep your body working properly, it's uncertain if there are any extra benefits to drinking when you're not thirsty.

It's often said that we need to drink eight glasses of water a day. A thorough review of the research found there was no evidence to support this and concluded that no one really knows precisely how much water we need. It's certainly true that our bodies need plenty of fluid, but this can come from milk, fruit juice, soft drinks and even the food we eat.

Water does have some advantages though. It contains no calories, which is useful if you're watching your weight, and there's no sugar in water, so it won't damage your teeth.

Tea, coffee and some soft drinks contain caffeine, which encourages your body to get rid of water in your urine. A healthy adult will get more water from these drinks than they lose, but it's a good idea to also drink some non-caffeinated drinks each day.

There's very little evidence about whether drinking extra water helps your kidneys clear toxins from your body. In the short term, extra water might help your body get rid of some substances, such as salt. But there's no research to tell us whether this would produce any real health benefits.

It's not clear whether getting plenty of water helps your other organs either. If you drink extra water, your body might just get rid of it in your urine. Some research suggests that water is more likely to stay in your body if you drink it slowly over several hours, rather than gulping it down quickly.

For people on a diet, it's sometimes suggested that drinking water can help fill you up, meaning you eat less. Again, there's surprisingly little evidence as to whether drinking water will help reduce calorie intake for people who are overweight. One small study found that people ate less when they were given food that contained more water, but drinking water separately with food made no difference.

Some people say they get headaches when they're dehydrated. One small study suggested that drinking plenty of water might help migraine sufferers get fewer headaches, but it only looked at 15 people, so it's hard to rely on the results.

Being very dehydrated can make your skin less elastic, but if you're healthy, there's no evidence that drinking lots of water improves the appearance of your skin.