Groundwater of Parque Rural del Nublo—UNESCO Biosphere Reserve and World Heritage Site “El Molinillo” Spring—Gran Canaria—Canary Islands—Spain

This study discusses the unique features of the rural park Parque Rural del Nublo (Gran Canaria) that resulted in the designation of this site as UNESCO’s Biosphere Reserve. Due to its indigenous flora and fauna, its mild climate and its farming lands, this park is considered as an outdoor “sustainable research laboratory”. This paper describes the main features (source, denomination, classification, municipality, year of declaration and hydro-chemical facies) of some of the many groundwater springs found in the park. The quality of the drinking water obtained from the spring “El Molinillo”, located in the basin of the municipality of Tejeda, is analysed by assessing its organoleptic, physico-chemical, chemical and bacteriological properties. Considering that it is described as “natural mineral water”, based on the taxonomy for mineral–medicinal waters, the water from “El Molinillo” is classified as hypothermal, alkaline and very soft water, with a low conductivity, a very weak mineralisation and a significant silica content. The water especially contains the following ions: bicarbonate, chloride, magnesium and calcium. The paper describes several pharmacological effects and therapeutic indications attributed to this water, analysing the impact of its silica content on human and plant health. The paper concludes that the park should be permanently protected as a World Heritage Site, and the water obtained from “El Molinillo” is classified as “drinking water”, “natural mineral water” and “mineral–medicinal water”.