Assessment of water, mainly for human consumption, is of key importance, as water is one of the main vehicles for disease. Distrust of water from the public supply system is one of the main factors leading to the use of alternative sources, such as potted water, on the understanding that this source is safe. This leads to an increase in mineral water consumption, mainly in 20 litre bottles, replacing water from public supply systems for consumption in homes, offices, businesses and schools. The aim of this study is therefore to contribute to increasing knowledge of the quality of mineral water of the main brands marketed in returnable packaging of 20 litres in the municipality of Picos — PI. On the basis of the physico-chemical analyses carried out with three marks of natural mineral water bottled in 20 litre bottles, values of chemical parameters different from those required by the legislation in force were found.