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Article

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

by
Eduardo Navarro
Centro de Hidrología y Climatología Médicas, Universidad del Atlántico Medio, C/Carretera de Quilmes 37, 35017 Las Palmas de Gran Canaria, Spain
Water 2025, 17(23), 3373; https://doi.org/10.3390/w17233373
Submission received: 7 October 2025 / Revised: 14 November 2025 / Accepted: 18 November 2025 / Published: 26 November 2025
(This article belongs to the Special Issue Groundwater for Health and Well-Being)
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Abstract

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”.

1. Introduction

Natura 2000 is the world’s largest coordinated network of protected areas, covering 27 Member States of the European Union, including Spain and, therefore, the Canary Islands. This electronic publication is issued by the European Environment Agency and is aimed at national and international experts and officers responsible for the preservation of terrestrial and marine biodiversity. This network of protected areas covers the highest valued and endangered species and habitats. The sites included in Natura 2000 are designated in accordance with the Birds and Habitats Directives. Many areas in Europe are increasingly suffering from a scarcity of clean water, an essential element for nature and for the health and wellbeing of people. Many of these areas to be preserved are located in the Canary Islands in general and on the island of Gran Canaria in particular. Nature 2000 is being continuously revisited and it was last amended on 28 February 2023 [1].
Rural parks are defined as wide natural spaces that comprise a natural, ecological and cultural landscape of public interest that need to be preserved and where farming, agricultural or fishing activities are carried out. These areas are classified as category V and VI in the nomenclature of the International Union for Conservation of Nature. The declaration of rural parks is intended to preserve the entire area and to promote a harmonious development of the local population, including the enhancement of their living conditions. The rural park Parque Rural del Nublo was declared as a “Natural Space” on 19 June 1987, whereas it was declared as a “Site of Scientific Interest” on 19 December 1987. On 29 June 2005, this rural park was declared a Biosphere Reserve by the International Council of the MaB Programme, entering the list of the Network of Natural Spaces of the Canary Islands (Gran Canaria C-11, Parque Rural del Nublo) [2]. The site known as Risco Caído and Montañas Sagradas de Gran Canaria Paisaje Cultural is located within Parque Rural del Nublo on a large mountain range that crosses the centre of Gran Canaria, with cliffs, ravines and volcanic rock formations that create a landscape characterised by its rich biodiversity. This area was recognised as a “UNESCO World Heritage Site” on 7 July 2019 [3]. Several municipalities comprising the park (Mogán and San Bartolomé de Tirajana) are characterised by their excellent climate and their internationally renowned thalassotherapy centres. Various groups from European countries such as the United Kingdom, Sweden, Norway, Denmark, Ireland, etc., usually do research on climatotherapy and balneotherapy in these centres. A research group from the Dermatology Centre of Malmö (Sweden) and from the University of Copenhagen (Denmark) recently conducted a clinical trial in the south of Gran Canaria on the psychosocial impact of climatotherapy on young patients with psoriasis [4].
In 1933, Gran Canaria had an inventory of 285 water springs. The number and volume of springs have now reduced, due to the intensive exploitation of the aquifers and climate change. The basin of the municipality of Tejeda, located within the park, comprises many ravines from which a wide number of springs emerge. The most significant springs, declared as fountains of “public interest”, include “El Molinillo” (declared of public interest in 2014), “La Mina” [5] (declared in 2014), “Túnel de Tejeda” (declared in 1999) and “Fuente Fría” (declared in 2002). All of them have similar physico-chemical and chemical features. These springs emerge through a thick basaltic layer that lies on another layer of tufa. Two further series of similar layers in terms of nature and thickness can be seen on the previous layers [6]. The spring “El Molinillo” was declared as a “Spring of Public Interest” and considered as “Natural Mineral Water” in the Official Gazette of the Canary Islands (BOC), dated 4 February 2014 [7] (Figure 1).
“El Molinillo” has been known as an important spring for a long time. It comes up in the ravine Barranco de Los Molinillos in the village of La Culata, within the basin of the municipality of Tejeda in the island of Gran Canaria. According to the Universal Transverse Mercator (UTM) system, the spring’s coordinates are as follows: UTM Regcan 95-WGS 84: X = 441.983 Y = 3.095.122 Z = 1.471. With a volume of 8–10 L/s depending on the climate seasons, its waters are used for local irrigation purposes and for the supply to the population in the municipality of Tejeda. A water mill known as “Molino de Agua de Los Manantiales” is located close to the source of the spring [8]. The mill was built on an area of a high scientific value, classified as a “rural land under natural protection”, and is registered in the Inventory of Ethnographic Heritage of the Council of Gran Canaria, known as Fondo para la Etnografía y el Desarrollo de la Artesanía de Gran Canaria or FEDAC (Fund for the Promotion of Ethnography and the Development of Craftwork of Gran Canaria). The mill was restored in the 1980s and currently receives a significant volume of visitors, exemplifying the typical rural houses that used to be built in the park (Figure 2).
This study’s aims are as follows:
  • Prove that Parque Rural del Nublo is significant at the regional, national and international level due to its unique ecological features and its biodiversity. This is why it was declared a UNESCO Biosphere Reserve on 29 June 2005. Later, on 7 July 2019, the 43rd session of the World Heritage Committee adopted the decision to inscribe the Cultural Landscape of Risco Caído and Montañas Sagradas de Gran Canaria on UNESCO’s World Heritage List.
  • Describe some of the autochthonous medicinal herbs found in Parque Rural del Nublo, which benefit from the good quality and high silica content of the waters that emerge in the park.
  • Value the work carried out by Centro de Plantas Medicinales de Tejeda (Centre of Medicinal Plants of Tejeda), first opened in 2007, which classifies and studies the phytochemicals of the plants in the park, many of which are used for therapeutic purposes in “complementary medicine” treatments.
This paper also describes some autochthonous species of the fauna in the park, some of which are in danger of extinction, requiring urgent measures such as population counts, recovery and protection actions.
  • Describe the most known springs in the park, specifying their features and analysing the quality of the groundwaters of the spring “El Molinillo”, based on their organoleptic, physico-chemical, chemical and bacteriological parameters.
  • Study the classification of the water as “drinking water” and “natural mineral water”, specifying its possible use as “mineral–medicinal water”, considering its potential pharmacological effects and therapeutic indications.

2. Materials and Methods

2.1. Study Area and Data

Parque Rural del Nublo is considered as an outdoor sustainability laboratory that covers the central and southwestern area of Gran Canaria, accounting for 43% of the surface of the island, in addition to over 35,000 marine hectares. Together with the rural park Parque Rural de Doramas, also located in Gran Canaria, these areas are considered as “sites of scientific interest”. The rural park Parque Rural del Nublo is the largest natural area on the island of Gran Canaria, located across the municipalities of Tejeda (first municipality of the Canary Islands that, in 2015, became a member of the association of the most beautiful villages in Spain), La Aldea de San Nicolás, Mogán, San Bartolomé de Tirajana, Artenara, Vega de San Mateo, Valleseco and Moya (Figure 3). The park covers around 27,000 hectares in the western area of Gran Canaria, which include around 30 small towns and villages.
Gran Canaria is one of the eight islands that comprise the Canary Islands archipelago. It is also the third island in terms of extension (almost 1560 km2) in the Canaries, after Tenerife and Fuerteventura, and the third island in terms of height, after Tenerife and La Palma. Gran Canaria is one of the four eastern islands in the archipelago, together with Fuerteventura, Lanzarote and La Graciosa. Its coordinates are latitude 28° north and longitude 15°35′ west. Gran Canaria is located 1250 km away from Cádiz, in Spain, with the European continental port closest to the island, and around 210 km away from the closest spot in the African coast. Within the Canary Islands archipelago, Gran Canaria lies between Fuerteventura, 83 km away on the east, and Tenerife, 62 km away on the west.
Gran Canaria has an extremely valuable natural heritage, in spite of its relatively reduced dimensions. With the uniqueness of its ecosystems, groundwaters, flora and fauna, its significant endemic species and its geology, many of its areas have been declared natural protected spaces. As of this writing, Gran Canaria is home to 33 protected natural spaces included in the European Union’s Natura 2000 Protected Area Network. Its wide range of natural and cultural elements includes the main symbol of the island, the volcanic monolith known as “Roque Nublo”, declared a “Natural Monument” (Figure 4).
Its rich natural heritage includes a mild climate throughout the year, a rich flora and fauna and a wide number of groundwater springs. Due to its latitude, Gran Canaria has a dry, warm climate, although the presence of the so-called “trade winds” provides the island with its unique features. As a result of these winds, the climate of the island varies based on the height, since the level of formation of clouds has an impact on its climate conditions. According to the “Hydrological Plans”, the highest islands (Gran Canaria, Tenerife and La Palma) with wet areas have an average rainfall of 740 mm/year. The climate variations within each island can be significant [9]. This is why Gran Canaria is commonly referred to as a “miniature continent”.
The forests of Canary Island pine trees (Pinus canariensis C. Sm.) are predominant in the wet areas of its mountains, although Californian pines (Pinus radiata D. Don) can also be found. This ecosystem is accompanied by almond trees (Prunus dulcis Mill), a typical species in the basin of Tejeda, with almonds being widely used for the preparation of traditional desserts. This jurisdiction is home to many small indigenous plant species, such as Teline microphylla D.C., Erysimum scoparium B. W., Sideritis dasygnaphala W.B. Isoplexis isabelliana (W. B., Artemisia thuscula Cav.), Euphorbia lamarckii subsp. Wildpretii., Rumex lunaria L., Salix Canariensis C. Sm. Ex LinK, etc. Many of these plants have therapeutic effects when prepared and administered as medicinal products. The livestock (mainly sheep and goats) live on highly nutritious species found in the fields of the park [10].
A recent publication has shown the phytochemical contents of Salix subserrata, finding the following compounds in the extracts of the plant: catechin, quercetin, saligenin, catechol, gallocatechin, salicin, triandriny and silicon. These compounds were extracted by standard methods using four different solvents and assessing the antioxidant activity in the leaves, the stem and the stem cortex. The EC50 (Effective Concentration 50) of the extracts was analysed using the DPPH (2,2-Diphenyl-1-picrylhydrazyl) assay and the silicon content of the stem was determined using a gravimetric method. The silicon content, the antioxidant activity, the Total Flavonoid Content (TFC), the Total Phenol Content (TPC) and the antimicrobial activity tests justify the important benefits of the Traditional Chewing Stick (TCS), made from the stem of Salix subserrata. Since oral health is the main determinant of the general health of the human body and over the 70% of the world’s population depends on traditional methods to maintain their oral health, Salix subserrata can be an alternative to the TCS, as it provides antimicrobial benefits and other advantages. Based on the EC50, the antioxidant activity of the leaves of Salix subserrata was similar to the standard reference compound used—ascorbic acid. The silicon content found in the extract of the plant stem was 0.24% [11]. Salix canariensis is an abundant endemic shrub in the Canary Islands that can be found in Parque Rural del Nublo. In the Canaries, it is usually known as “sauce” (willow) [10]. Ethnobotanical evidence shows that the flowers, leaves, sprigs and cortex of this shrub have been used to prepare infusions intended to relieve different kinds of pain. Several extracts of Salix canariensis have been used to obtain tanins and phenolic glycosides, such as salicin, due to its proven analgesic and anti-inflammatory activity [12]. It is also known that many species of the genus Salix contain poliphenols, salicylates expressed as salicin, tanins, etc., and these compounds have an anti-nociceptive, anti-inflammatory and antipyretic effect [13]. The presence of silicon has not been described in any of the species of the genus Salix reviewed (Salix daphnoides, Salix fragilis, Salix purpurea, Salix canariensis), except for the species Salix subserrata. The Centre of Medicinal Plants of Tejeda aims to study the phytochemical properties of Salix canariensis to identify the compounds present in different extracts of the plant and to determine the presence of silicon.
The area has a large endemic fauna that makes it unique in comparison to other areas in Macaronesia, the region made up of four archipelagos: the Canary Islands, Azores, Madeira and Cape Verde. The park is characterised by the absence of large vertebrates and of dangerous or venomous species. Its vertebrates include the lizard species Gallotia stehlini, the skink Chalcides sexlineatus Steindachner, the gecko Tarentola delalandii and the shrew Crocidura russula [14]. Birds are, however, the most numerous and representative animals of Gran Canaria’s fauna. The nesting birds in the island comprise 48 species, with autochthonous birds such as the robin Erithacus rubecula, the woodpecker Picidae and the finch Fringilla polatzeki. The Atlantic canary (Serinus canaria), popular in the Canary Islands for its singing skills, must be pointed out due to its establishment in the archipelago, becoming a symbol of both the Canary Islands and of Gran Canaria in particular. The park is also an important resting place for migratory birds coming from Europe on their way to Africa. These birds include marine nesting species, especially Scopoli’s shearwater (Calonectris diomedea) [15].
The municipalities covering the park develop activities that respect the environment, the training, the leisure and the traditional use of natural resources, as well as rural tourism. For instance, the municipality of Tejeda is well known for the preparation of traditional food products, such as biscuits, almond shortbreads (polvorón), lard-based cookies, almond cakes and the popular marzipan of Tejeda. In addition, this municipality features a reference research site known as Centro de Plantas Medicinales de Tejeda (Centre of Medicinal Plants of Tejeda), opened in 2007 with 5000 square metres aimed at the recovery, study and dissemination of knowledge about the relationship between humans and nature through the use of plants, remedies and beliefs. In addition, Artenara is home to an important reference centre used as a “Nature Study Centre” (Aula de la Naturaleza), equipped with Environmental Education tools.
The park follows the rules of the Man and the Biosphere Programme (MaB Programme) established by UNESCO in 1970, which promotes the conduct of interdisciplinary research in natural and social sciences and the training on natural resource management, especially with regard to the preservation and the sustainable use of biodiversity. Thus, the MaB Programme not only contributes to a better understanding of the environment, but also to a stronger commitment by science and scientists to the development of policies intended to make a rational use of biological and cultural diversity, including a global change. On 29 June 2005, the terrestrial area located in the southwest of Gran Canaria and a large marine strip known as Parque Rural del Nublo were declared a Biosphere Reserve by the International Coordinating Council of the MaB Programme [16] (Figure 5).
Groundwaters come up from a large number of spots (either as galleries, springs, wells or drills) in Parque Rural del Nublo. Table 1 shows the basic characteristics of some of the groundwaters collected in the park, considered as “drinking water” and “natural mineral water”. Some of these groundwaters are also described as “mineral–medicinal water”, given their use in balneotherapy. Apart from being used for human consumption, a significant volume is also bottled to be distributed across the Canary Islands.

2.2. Water Samples Collection

A total of 12 samples of water were taken at the outlet of the spring “El Molinillo” (municipality of Tejeda, island of Gran Canaria) from May 2022 to April 2023. On a monthly basis, the samples were collected and kept in a 2 L sterile container and subsequently sent to a laboratory in order to analyse the water’s organoleptic, physico-chemical, chemical and bacteriological properties.

2.3. Characteristics of Groundwater Water and Organoleptic Analysis

The temperature, the pH and the yield at the outlet of the spring “El Molinillo” were also measured. The organoleptic parameters (colour, odour and taste) were assessed as per the standard procedures [17].

2.4. Physico-Chemical and Chemical Analysis

“Natural mineral waters” are described as bacteriologically healthy waters that emerge from an underground stratum or formation and can be obtained from a spring. Alternatively, these waters can be artificially taken through drilling operations, through a well or a gallery or by a combination of these methods. They can be clearly distinguished from other ordinary drinking waters due to (1) their nature, characterised by their concentration of minerals, trace elements and other compounds and, occasionally, by specific biological effects; (2) their chemical consistency; and (3) their original purity [18]. The physico-chemical parameters were determined in the laboratory using the following analytic techniques/standards: potential Hydrogen (pH) Electrometry; Conductivity at 25 °C (microS.cm−1) Electrometry; Total organic Carbon (mg C/L) UNE-EN ISO 20236:2022 [19]; Total hardness (mg/L CaCO3) Complexometry EDTA; Silica (mg SiO2/L) Spectrophotometry UV-VIS SM4500E; dry residue at 180 °C (mg/L) Gravimetry—the dissolved substances analysed were expressed in mg/L; anions: bicarbonate (Photometry DIN 38405-D17) and chloride ion chromatography UNE-EN ISO 10304-1 [20]; nitrate and nitrite ion chromatography UNE-EN ISO 10304-1 [20]; sulphate UNE-EN ISO 10304-1 [20], carbonate UNE-EN ISO 9963-2 and fluoride ion chromatography UNE-EN ISO 14911 [21]; cations: calcium, magnesium and potassium ion chromatography UNE-EN ISO 14911 [21]; sodium chromatography UNE-EN ISO 14991 [21]; and ammonium Titration SM2320.

2.5. Diachronic Chemical Constancy

The diachronic consistency of the main chemical compounds was assessed using the samples taken throughout a 12-month period. This parameter analyses the consistency of the concentration of the main chemical compounds in the water over time, as this is an essential requirement of natural mineral waters and of mineral–medicinal waters [17].

2.6. Bacteriological Analysis

These microbiological parameters were studied in the laboratory following the standard procedure: Colony count at 22 °C/72 h (cfu/mL); Colony count at 37 °C/72 h (cfu/mL); Coliform bacteria (cfu/250 mL); Eschreichia coli (cfu/250 mL); Salmonella spp. (in 250 mL); Faecal Streptococci (cfu/250 mL); Sporulated sulphite-reducing anaerobes (ufc/50 mL); and Pseudomonas aeruginosas (ufc/250 mL); (cfu) = colony forming units [22].

3. Results

3.1. Characteristics of Groudwater and Organoleptic Analysis

The average temperature at the spring “El Molinillo” was 18 °C, with a pH = 7.5 and a water flow ranging from 8 to 10 L/s. The water that spontaneously flows up is transparent (colourless) and has no smell (odourless) and no abnormal taste (insipid). The most frequent organoleptic features of the springs located in the municipality of Tejeda and in the Parque Rural del Nublo are described below.

3.2. Physico-Chemical and Chemical Analysis

Table 2 shows the maximum, minimum, mean, standard deviation and parametric values for drinking water and mineral natural water in “El Molinillo”. We analysed 12 water samples (n = 12).

3.3. Predominant Dissolved Substances (Chemical Analysis)

Figure 6 shows the average value of the main dissolved substance parameters expressed in mg/L: Anions: bicarbonate = 45.2; chloride = 9.6; nitrate = 6.8; and sulphate = 2.1. Cations: calcium = 7.6; sodium = 6.6; magnesium = 5.4; and potassium = 1.5. These parameters were converted into meq/L and % meq/L. These parameters show balanced waters, a feature observed upon comparing the similarities between the total anions and total cations. Ʃ anions (meq/L) = 1.15 and Ʃ cations (meq/L) = 1.13. This is an indication of ionic balance, usually linked to high-quality waters. However, the quality of the water also depends on other factors, such as the presence of some specific beneficial ions or the absence of contaminants. This ionic balance is remarkable, because it shows that the concentrations of the different ions are in harmony, a condition that can be beneficial both for health and cell functions.

3.4. Bacteriological Analysis

Table 3 shows the bacteriological health characteristics of the water from El Molinillo, including the parameters studied, results, parametric values and units. It can be seen that it is bacteriologically healthy water.

4. Discussion

Regional, national and international researchers have visited Parque Rural del Nublo to study its geology, climate, hydrography, ecology (relations between living organisms) and biodiversity (flora, fauna, fungi, microorganisms, genetic variability, etc.). Many of these researchers have visited the area with the support of the research centre “Jardín Botánico Viera y Clavijo”, founded in Gran Canaria in 1952. For instance, one of Gran Canaria’s endemic species that has been recently studied is Sideritis dasygnaphala, an herb with medicinal properties that relieves cough and stimulates the circulatory system. The preservation status of this species is a current matter of research [23]. The groundwaters and their extensive exploitation in Gran Canaria, as well as their hydrological, economic and ethical impact, have also been addressed [24]. Furthermore, the groundwaters of Gran Canaria, due to their high silica (SiO2) content, have a significant balneotherapeutic potential that needs to be explored. Testing the health benefits of these silica waters in human beings through balneotherapy seems to be promising. Hydro-geochemical methods, including geochemical modelling, can provide effective tools for the protection of these medicinal waters [25].
The water from the spring “El Molinillo” was collected in a sterile container following the recommendations set out in the 23rd edition of Standard Methods for the Examination of Water and Wastewater [26]. The physico-chemical and chemical parameters were assessed based on the parametric values established in the handbook of Spanish mineral-medicinal waters (Vademécum III de Aguas Minero-Medicinales Españolas) [17]. It was observed that the spring “El Molinillo” meets the physico-chemical, chemical and bacteriological parameters established in the World Health Organization’s Guidelines for Drinking-Water Quality. Therefore, this water is useful for drinking purposes. Due to its ionic balance, it has a beneficial impact on human health. In general, the concentration of ions found in the drinking water does not result in health problems [22]. Considering the pH of this natural mineral water, it is defined as alkaline water. It is also described as hypothermal water, considering its temperature at the outlet of the spring. Based on its mineralisation, it is classified as low-conductivity water and, according to its hardness, it is described as soft water. The dry residues found classify it as low-mineralisation water. And, based on the silica contents, it is described as silica water [17]. Its organoleptic and physico-chemical features are similar to those of the mineral water marketed by Fuenteror, which flows out from a spring located in the vicinity of the basin of Tejeda [27]. The analysis of the substances dissolved in the water shows that the most significant anions are bicarbonate and chloride, whereas the predominant cations are magnesium and calcium. This water is described as “natural mineral water” with a low mineralisation and a healthy bacteriological profile [18]. Although a part of this water is used for irrigation purposes in Parque Rural del Nublo, it is also used to supply drinking water to the municipality of Tejeda.
Based on its physico-chemical, chemical and bacteriological features, the spring “El Molinillo” is classified in section (B) of the Spanish Mining Act and is considered as “Mineral–Medicinal Water”, under the category of “Natural Mineral Water”. This is why this spring was declared as a fountain of “public interest”, as published in the Official Gazette of the Spanish State and in the Official Gazette of the Canary Islands [18]. Since this type of water is described in all the mineral–medicinal water nomenclatures as “low-mineralisation water”, various pharmacological actions and therapeutic effects can be attributed to it [28,29]. Considering its low mineralisation and low temperature (the water flows out at a temperature below 20 °C), this water especially causes a diuretic effect when given orally. Therefore, it is indicated for urinary infections, as it facilitates the expulsion of urine, preventing fluid retention in the urinary tract. It is also recommended for sub-acute and chronic non-hydropigenic glomerulonephritis and for the chronic inflammation of the urinary tract (cystopyelitis, cystitis, urethritis, etc.). For renal lithiasis, it can also be useful, as it can change lithogenic factors locally (infections, acid–base balance disorders, etc.). In a crenotherapeutic context, this type of water is given orally at relatively high doses (600–1800 mL) 3 times/day, with the patient taking the dose within a period of 30–60 min in the morning on an empty stomach and in a prone position (to help the water flow through the hepatic portal system). Its main components may have a very mild added value in terms of vasodilation, improving heart rate disorders in diabetic patients and helping to prevent and treat kidney stones (oxalate and calcium carbonate), as well as chronic infections of the urinary tract [28,29]. Considering its sodium content (Na+ = 6.8 mg/L), it is also indicated for the preparation of food for babies. It is well known that water is one of the main components of a baby’s diet. The water quality plays an important role in the safety of foods, especially for babies. For young children, groundwater can be used, provided that it is free of chemical and microbiological contamination and has the appropriate chemical composition. For babies, however, natural spring water and natural mineral water with a low sodium level (<20 mg/L Na+) and a low mineralisation (<500 mg/L of total dissolved solids or TDS) are recommended. For older children, the mineralisation of the water can be higher (500–1000 mg/L). The bioavailability of macro- and microelements in the water is high, so mineral water can be a good source of these elements in the diet of children [30]. The US Environmental Protection Agency also recommends that the sodium concentration in water should not exceed 20 mg/L [31].
On the other hand, silica waters are described as water with a concentration of SiO2 > 30 mg/L. The silica level in the water obtained at the spring “El Molinillo” is SiO2 = 41.2 mg/L. Therefore, this water is classified within the group known as “silica waters”. Some studies find that the daily amount of silicon required for adults ranges from 20 to 50 mg/day [32]. Other research works state that the intake of silicon (Si, approximately 30 mg/day) is one the highest amounts of trace elements required for humans [33]. The intake of silicon obtained from non-alcoholic drinks, cereal-based food products and carotene-rich vegetables was also positively linked to serum silicon levels. These results may help establish dietary silicon recommendations and develop practical advice on dietary options to ensure an appropriate supply of silicon. In any case, the result of this study should be confirmed with further large-scale epidemiological research studies [34]. Many mineral waters contain less than 10 mg/L of silica, whereas others may contain up to 80 mg/L. Volcanic waters have a significant amount of silica, and the Canary Islands are volcanic islands. An example of the mineral water of Gran Canaria that meets these characteristics is Aguas Fuenteror, with a SiO2 concentration of 57.7 mg/L [27]. Almost all of the mineral waters in the Canary Islands can be classified as siliceous, and the importance of silicon for the human body increases as the body ages (from 40 years onwards). The skin and the connective tissue of the arteries, bones and cartilage become more and more fragile and lose silicon. The administration of silicon as SiO2 (silica) dissolved in water as a dietary supplement is becoming a matter of study for many researchers. There are convincing data suggesting that silica is essential for human health. Silica deficiency induces deformities in the skull and the peripheral bones, poorly formed joints, reduced contents of cartilage and collagen and the disruption of mineral balance in the femur and vertebrae. Although very little toxicity data have been found regarding aqueous silica consumption due to, in part, the lack of toxicity reports and the general presumption of safety, a few studies conducted on rodents show that a concentration level of 50,000 ppm (mg/L) of dietary silica had no adverse effects. This substance is recommended by many experts as an essential mineral that provides a healthy appearance and facilitates the proper maintenance of the body [35].
For European individuals, the average intake of silicon ranges from 25 to 50 mg/day [32,36], whereas 1 litre/day of water from “El Molinillo” contains 42.5 mg/L of silica (approximately 20 mg of Si). Therefore, 1 L/day of water from “El Molinillo” matches the average intake range and can contribute to the recommended daily intake of silica, which is not well defined yet, suggesting that the daily supplementation of this silica water can be highly beneficial for human health. Furthermore, it has been observed that the use of hydrophobic silica has not produced adverse effects on health. For rodents, the LD50 is >7.9 g/kg of body weight [37]. It is also known that silica is found in various plants and herbs, as well as in fibre-rich foods, including whole grain cereals, rice, fruits and vegetables. For instance, even though colloidal silica acid, silica gel and zeolites are relatively insoluble in water, they can increase the concentration of soluble silica in water and they are believed to depend on specific physico-chemical characteristics. Overall, the supply of foods provides sufficient silicon in the forms set out above, can be absorbed by the body and can improve human health significantly [38]. The solubility limit of silica is approximately 2–3 mM at the relatively neutral intestinal pH. Drinking water and other drinks, including beer, have total concentrations of Si below 2 mM and, therefore, they mostly contain the soluble monomeric forms that result in a high gastrointestinal absorption [39]. A healthy diet rich in these foods is an excellent way of taking in the ¨Ñ that the body needs. It should be considered, however, that more and more people depend on pre-cooked and processed food products that lack silica and other important nutrients. In addition, the modern refination methods eliminate silica from some foods, reducing the daily intake of this element. Animal trials have proven that the results of a cognitive test are positively correlated to the intake of silica, and the risk of suffering from Alzheimer’s disease (AD) is reduced in the subjects with a higher intake of silica in comparison to other subjects. Silica is probably the natural antidote to aluminium and may have a beneficial effect by diminishing the bioavailability of aluminium, whose neurotoxicity has been clearly established [40]. The chronic intake of aluminium increases systemic and peritoneal inflammation and the dysfunction of the plasma membrane. Considering that silicon is a natural antagonist for aluminium, the presence of high levels of silicon in drinking water re-established the secretion of IL-10 and TNF-α in the plasma membrane, preventing a lasting inflammation. Therefore, the intake of silicon as silica can reduce the immunotoxicity caused by aluminium [41].
It is also well known that Si plays a beneficial role in the development of drought tolerance in various plants. This effect may be due to the plant’s capacity to accumulate a significant volume of Si and to use it for osmoregulation purposes, resulting in a self-evident improvement in the photosynthesis and the antioxidant enzymatic activity of the plant [42]. Silicon (Si) is abundant in the lithosphere, and previous studies have confirmed that it plays an important role in the growth of plants. Higher plants absorb soluble silicon from the soil through the roots, and the substance is stored in the plant tissues, especially in form of phytoliths [43]. For assessing the pharmacological and phytotherapeutical effects of plants, the silicon content is more and more significant. This may give rise to the study of this medicinal herb in order to assess its pharmacological effects again and to find out its content of silicon, an element that mainly comes from the concentration of silica in the groundwaters of the park.

5. Conclusions

It can be concluded that Parque Rural del Nublo is an ecosystem that must be preserved as a heritage site due to its unique geological and hydrographic features and its flora and fauna, as well as for its declaration as a UNESCO Biosphere Reserve and World Heritage Site. The major dissolved substances (bicarbonate, chloride, nitrate, sulphate, magnesium, calcium, sodium and potassium) were expressed in mg/L and must be converted into meq/L and % meq/L in order to classify the waters based on their ionic balance and on their potential interest for human health. Overall, the concentrations of ions found in the drinking water do not pose any risks to human health. Based on its physico-chemical, chemical and bacteriological parameters, the water flowing up from the spring “El Molinillo” is considered as “drinking water” and also as “natural mineral water”. Thus, it must be protected against any kind of contamination. Its properties as “mineral–medicinal water” can be beneficial to treat some human medical conditions, including those caused by renal disorders or silica deficiency. Hence, its use for balneotherapy purposes should be assessed. The content of silica also plays an important role in the health of the diversity of the endemic plants of the rural park, so the preservation of this ecosystem is required. Establishing a station to bottle the water from the spring “El Molinillo” in an appropriate location within the rural park would help monitor the quality of the water, would create employment in this protected space and would prevent depopulation in this area. It is necessary to continue to assess the quality of the groundwaters across the park as a response to the threats posed by anthropogenic and geogenic contaminants. This would provide an overview of the groundwaters found in this area that could be made extensive to the entire island of Gran Canaria.

Funding

This research received no external funding.

Data Availability Statement

The details of the geographical coordinates and the maps have been obtained from the mapping company GRAFCAN (Cartografía de Canarias, S.A. Las Palmas de Gran Canaria, Spain) https://visor.grafcan.es/, accessed on 15 June 2025.

Conflicts of Interest

The author declares no conflicts of interest.

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Water 17 03373 g001
Figure 1. Spring of “El Molinillo”.
Figure 1. Spring of “El Molinillo”.
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Figure 2. Los Manantiales water mill.
Figure 2. Los Manantiales water mill.
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Figure 3. Picture of Gran Canaria and municipalities of Nublo Rural Park and its location in the Atlantic Ocean facing Africa: 1, Tejeda; 2, Artenara; 3, La Aldea de San Nicolás; 4, Mogán; 5, San Bartolomé de Tirajana; 6, San Mateo; 7, Valleseco; 8, Moya. The location of the geographical coordinates has been specified.
Figure 3. Picture of Gran Canaria and municipalities of Nublo Rural Park and its location in the Atlantic Ocean facing Africa: 1, Tejeda; 2, Artenara; 3, La Aldea de San Nicolás; 4, Mogán; 5, San Bartolomé de Tirajana; 6, San Mateo; 7, Valleseco; 8, Moya. The location of the geographical coordinates has been specified.
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Figure 4. “Roque Nublo” monolith and Tejeda basin.
Figure 4. “Roque Nublo” monolith and Tejeda basin.
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Figure 5. Gran Canaria Island and Nublo Rural Park.
Figure 5. Gran Canaria Island and Nublo Rural Park.
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Figure 6. Major components of water from “El Molino” (meq/L and % meq/L).
Figure 6. Major components of water from “El Molino” (meq/L and % meq/L).
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Table 1. Basic characteristics of some springs in the Nublo Rural Park.
Table 1. Basic characteristics of some springs in the Nublo Rural Park.
OrigenDenominationMunicipalityClassificationDeclaration YearGeographical CoordinatesHydrochemical Facies
GEl MolinilloTejedaNMW2014X = 441.983MgCO3H
Y= 3095.122
SLa MinaTejedaNMW2014X = 441.891MgCO3H
Y= 3096.511
GTúnel de TejedaTejedaNMW1999X = 448.147CaCO3H
Y= 3104.745
STaguiguiTejedaNMW1996X = 448.160NaCO3H
Y= 3104.811
SLa Fuente FríaTejedaNMW2002X = 448.697NaCO3H
Y= 3104.819
SLa FloridaS. Bartolomé de TirajanaNMW2000X = 460.622NaCl
Y= 3085.701
SManantial de SorruedaS. Bartolomé de TirajanaNMW2000X = 447.323Na CO3H
Y= 3084.609
SLa RosianaS. Bartolomé de TirajanaMMW1995X = 445.606NaCl
Y= 3088.297
WEl Zumacal IIVallesecoNMW1998X = 444.201NaCO3H
Y= 3103.539
WSan AntónVallesecoNMW1997X = 444.495NaCO3H
Y= 3105.552
WLa GambuesillaVallesecoNMW2002X = 420.084NaCl
Y= 3096.687
GLa UmbridilllaMogánNMW2022X = 427.055NaCO3H
Y= 3081.837
GHuerta del MolinoSan MateoNMW1995X = 447.885NaCO3H
Y= 3098.259
Note: Source: Own elaboration; G = gallery; S = spring; W = well; NMW = natural mineral water; MMW = medicinal mineral water.
Table 2. Parameters studied for spring “El Molinillo”. Natural Mineral Water.
Table 2. Parameters studied for spring “El Molinillo”. Natural Mineral Water.
ParametersMaximumMinimumMeanStandard DeviationParametric Value for Mineral Natural Water
pH7.707.407.520.065.5–9.5
Alkaline water
Conductivity at 25 °C (µS.cm−1)1161101122.06100–200
Low conductivity water
Dry residue at 180 °C (mg/L)1141011084.88100–250
weak mineralisation water
Total hardness (mg/L CO3Ca)43.838.642.31.500–50
Very soft water
Total organic Carbon
(mg C/L)		<0.1<0.1<0.1->5 mg/L
Organic Matter Indicator
Silica (mg SiO2/L)42.038.641.81.29>30 mg/L
Silica water
Bicarbonate (mg HCO3/L)46.442.945.21.27250 mg/L
Carbonate (mg CO3/L)<1.2<1.2<1.2--
Sulphate (mg SO4/L)2.32.02.10.29<250 mg/L
Chloride (mg Cl/L)10.29.29.60.27<250 mg/L
Nitrate (mg NO3/L)6.96.36.80.28<50 mg/L
Fluoride (mg F/L)<0.1<0.1<0.1-<1.5 mg/L
Nitrite (mg NO2/L)<0.01<0.01<0.01-<3 mg/L
Ʃ anions (meq/L)1.191.101.15
Calcium (mg Ca/L)8.67.47.60.36<150 mg/L
Magnesium (mg Mg/L)6.05.05.40.31<50 mg/L
Sodium (mg Na/L)7.16.56.60.31<200 mg/L
Potasium (mg K/L)1.71.41.50.30
Amonium (mg NH4/L)<0.10<0.10<0.10-<0.20 mg/L
Ʃ cations (meq/L)1.161.121.13
Table 3. Bacteriological characteristics of “El Molinillo” spring.
Table 3. Bacteriological characteristics of “El Molinillo” spring.
ParameterResultParametric ValueUnits (cfu/mL)
Colony count 22 °C/72 h<3-----(cfu/mL)
Colony count 37 °C/72 h<3-----(cfu/mL)
Coliform bacteria00(cfu/250 mL)
Eschreichia coli00(cfu/250 mL)
Salmonella spp.absenceabsence(in 250 mL)
Faecal Streptococci00(cfu/250 mL)
Sporulated sulphite reducing anaerobes00(cfu/50 mL)
Pseudomonas aeruginosa00(cfu/250 mL)
Note: (cfu) = (colony forming units).
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Navarro, E. Groundwater of Parque Rural del Nublo—UNESCO Biosphere Reserve and World Heritage Site “El Molinillo” Spring—Gran Canaria—Canary Islands—Spain. Water 2025, 17, 3373. https://doi.org/10.3390/w17233373

AMA Style

Navarro E. Groundwater of Parque Rural del Nublo—UNESCO Biosphere Reserve and World Heritage Site “El Molinillo” Spring—Gran Canaria—Canary Islands—Spain. Water. 2025; 17(23):3373. https://doi.org/10.3390/w17233373

Chicago/Turabian Style

Navarro, Eduardo. 2025. "Groundwater of Parque Rural del Nublo—UNESCO Biosphere Reserve and World Heritage Site “El Molinillo” Spring—Gran Canaria—Canary Islands—Spain" Water 17, no. 23: 3373. https://doi.org/10.3390/w17233373

APA Style

Navarro, E. (2025). Groundwater of Parque Rural del Nublo—UNESCO Biosphere Reserve and World Heritage Site “El Molinillo” Spring—Gran Canaria—Canary Islands—Spain. Water, 17(23), 3373. https://doi.org/10.3390/w17233373

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