More than 90% of beer is water. Thus beer can make a contribution to the daily fluid supply, which has to be at least 1.5 to 2 litres a day. But be careful, alcohol also has a dehydrating effect which means that beer (and wine and spirits) cannot be the only source of fluid. 

Alcohol-free beer has less of a dehydrating effect than ordinary beer, but still causes a greater loss of fluid than water. This was shown in a study on 23 professional footballers who after training were given either 75 cl of alcohol free beer or the same quantity of water. Urine collections over the next two hours showed that the group that drank the alcohol-free beer lost 22% of the original quantity, while the water drinkers lost 17% in the same time span. This small difference is probably explained by the small quantity of alcohol in so-called alcohol-free beer (alcohol-free beer can contain up to 0. 5% alcohol). 

Brewers have long been aware that extremely pure water has to be used for beer. For every litre of beer, 7 to 10 litres of water are needed, for the brewing itself and for cleaning and sterilising all the receptacles that the beer is produced and transported in. Every country, including Belgium, has strict rules on the water used for brewing beer. These rules relate to the shelf life, acidity, salt content, oligo-elements, and any contaminants, including pollutants. The pure water used in beer also reduces the risk of some cancers such as bladder cancer.

Source: beer&