According to the American Dental Association, bottled mineral water does not contain sufficient levels of fluoride to prevent cavities, especially in young children. Studies have shown that drinking fluoridated water can reduce caries by as much as 40%. Even though adding fluoride to tap water is a cost-effective public health measure, in the UK, only 10% of the population receives fluoridated tap water, as opposed to more than 50% in the US. Although many children now take bottled water to school, few bottled waters contain sufficient levels of fluoride to be effective against tooth decay. Under British law, fluoride in natural mineral water must be labelled where it has exceeded 1.5 mg per litre, with a maximum allowed fluoride limit of 5 mg/l. A study published in the BDJ in 2003 concluded that bottled water is unlikely to make an important contribution to total fluoride intake in British diets.