Water/fluid Water or fluid is a vital component of our diets, even though it's not considered a specific nutrient.

In this article

Why do we need water? How much do we need?

Bottled water Is it necessary to buy bottled water?

Water makes up 50 to 70 per cent of an adult's total body weight and, without regular top-ups, our body's survival time is limited to a matter of days.

Water's essential for the body's growth and maintenance, as it's involved in a number of processes. For example, it helps get rid of waste and regulates temperature, and it provides a medium for biological reactions to occur in the body.

Water's lost from the body through urine and sweat, and must be replaced through the diet. If you don't consume enough you can become dehydrated, causing symptoms such as headaches, tiredness and loss of concentration. Chronic dehydration can contribute to a number of health problems such as constipation and kidney stones.

The body gets its fluid from three sources:

• Drinks, either plain water or as part of other beverages including tea, coffee and squash
• Solid foods, especially fruit and vegetables (even foods such as bread and cheese provide small amounts of fluid)
• As a by-product of chemical reactions within the body

Most healthy adults need between one and a half to three litres a day, so aim to drink six to eight medium glasses of fluid daily. Beverages such as tea, coffee and fruit juices count towards fluid intake, and may bring with them other nutrients or benefits.

You may require more fluid if you're very physically active or during periods of hot weather.

You can judge whether you're drinking enough by the colour of your urine. If it's a pale straw colour then your fluid intake is probably fine. If your urine is dark yellow, you probably need to drink more.

How to maintain fluid levels

• Start as you mean to go on, with a glass of water when you wake.
• Find time to make yourself regular drinks during the day - don't forget that tea, coffee and juices can count. Just watch out for the amount of sugar consumed in some soft drinks.
• Keep a bottle of water in your bag, as it's a convenient way of providing fluid if you're travelling or exercising.
• Get into the habit of having a glass of water with every meal.
• The sensation of thirst is not triggered until you're already dehydrated, so it's important to drink before you get thirsty.
• Increase your intake of fresh fruit and vegetables, as they have a high water content.

There are two types: spring water and mineral water.

Spring water is collected directly from the spring where it rises from the ground, and must be bottled at the source. UK sources of spring water must meet certain hygiene standards, and may be further treated so they meet pollution regulations.

Mineral water emerges from under the ground, then flows over rocks before it's collected, resulting in a higher content of various minerals. Unlike spring water, it can't be treated except to remove grit and dirt. Different brands of spring and mineral waters have differing amounts of minerals depending on their source.

The drinking water available from UK taps is perfectly adequate to replenish fluid loss, and undergoes many processes to bring it up to the standards set out in the UK Water Supply Regulations.

In some areas tap water has fluoride added, which can reduce the risk of dental decay.

There are certainly no proven health benefits of bottled water over tap water. Although there are growing concerns about the sustainability of bottled water, ultimately it comes down to personal choice.

This article was last medically reviewed by the MRC Human Nutrition Research in July 2008.
First published in March 2001.