Sources of water in the diet
It has been estimated that roughly 20% of water consumed is from food, and the remaining 80% from beverages. The water content of food varies widely; it is usually less than 40% in cereal products, 40-70% in hot meals, more than 80% in fruits and vegetables, and approximately 90% in human breast milk and cows’ milk.
We can get our fluid requirements from a number of sources as water is contained in most foods and all drinks consumed. It is not necessary to drink only ‘pure’ water, although this is a good choice. Other drinks such as squash, fruit juice, fizzy drinks, tea and coffee contribute to our daily requirements too. Like everything we consume, selection depends on personal preference and availability. In addition to their contribution to our water needs, beverages may also have a wider effect on our health. Some, such as fruit juice, milk and tea contain nutrients and other substances that are beneficial for health. However, it is important to be aware of the sugar and overall energy content of beverages. Drinking a lot of energy-containing beverages may cause over consumption of energy, potentially leading to weight gain and obesity.
Dental health is also a consideration, and frequently consuming beverages containing sugar, such as fruit juices and sugar-containing fizzy drinks, can increase the risk of dental caries. In addition, dental enamel erosion can be caused by frequent consumption of acidic beverages, such as fruit juices and carbonated beverages.
Caffeine is a mild diuretic (in that it increases urine output to a small extent), but drinks that contain caffeine (such as tea, coffee, cola) also contribute to fluid intake under normal circumstances. You do not need to drink more water to compensate for the caffeine present in these drinks. Women who are pregnant should limit their caffeine intake to 200mg/day or less .This is because high levels of caffeine can result in babies having a low birth weight, or even lead to pregnant mothers miscarrying.
Other caffeine-like substances are present in chocolate (theobromine) and tea (theophylline) which also have a mild diuretic effect.
With alcoholic drinks, the dehydrating effect can be greater, depending on the type of drink consumed. Spirits consumed alone can cause dehydration, while more dilute alcoholic drinks such as shandy can have a net hydrating effect. Drinking water alongside alcoholic drinks will minimise any dehydrating effects. It is important to take account of safe guidelines for drinking.
Bottled, filtered or tap water?
A large number of bottled waters are now available, some of which are flavoured, carbonated and/or have added vitamins and minerals. Bottled waters are a convenient way to keep hydrated and are recommended where a clean, safe water supply cannot be guaranteed, for example when travelling abroad. There are no significant nutritional differences between bottled and tap water in the UK, and regulations can be tighter for tap than bottled water.
Some people choose to drink filtered water because they prefer the taste, odour and colour. Filtering water decreases its hardness and so reduces the scum sometimes seen on the surface of hot drinks. The filtering process also reduces chlorine along with other impurities in the water, which may affect taste, but filtered water offers no special benefits in terms of nutrition.
Tap water in the UK is safe to drink. Boiled and cooled water is recommended when making up infant formula.
Hard and soft water
Water naturally contains dissolved minerals such as calcium, magnesium and potassium. These minerals are picked up by rain water as it passes through the ground. If water seeps through hard rocks (such as granite) or peaty soils, it does not pick up these minerals. But, if water seeps through soft rocks, such as chalk and limestone it picks up both calcium and magnesium.
Water that contains lots of calcium and magnesium is called hard water and causes deposits to develop in kettles and other household equipment. Water with low levels of these minerals is known as soft water.
It has been suggested that one of the health benefits of drinking hard water may be a protective effect against cardiovascular disease and stroke. However, results from a number of studies have been inconsistent and the risk of developing cardiovascular disease is more strongly influenced by other factors such as high blood pressure and cholesterol, and smoking, diet, obesity, alcohol and physical activity.