Quality and Influences of Natural and Anthropogenic Factors on Drinking Water in Rural Areas of Southern Chile

Abstract

Water quality is a fundamental aspect of public health and environmental sustainability. In rural areas, the physicochemical and microbiological quality of drinking water depends not only on hydrogeological conditions but also on anthropogenic activities carried out on the surface of the basin. This study aimed to identify natural and anthropogenic influences related to the quality of drinking water in rural areas of southern Chile. In order to perform this, six rural drinking water systems were evaluated. A total of two types of catchment sources (groundwater and surface water) that were located in a longitudinal gradient were used, where coverage and sequences of rocks and soils could be differentiated. The results show that the water delivered by the majority of rural drinking water systems studied was of good quality, meeting the standards of Chilean and international regulations. No fecal coliforms or Escherichia coli were recorded. In addition, we recorded that turbidity, color, pH, concentration of total dissolved solids and fecal coliforms showed significant differences between groundwater and surface water. We also recorded that in two groundwater systems, iron and manganese levels slightly exceeded the regulations, endangering the acceptability of the water. These increases can be related to the natural origins of the metals, linked to the presence of oxides in Andisol- and Utisol-type volcanic soils.

1. Introduction

The quality of drinking water sources is essential for human health and is one of the main technical and administrative challenges that countries must implement to meet the health needs of rural localities [1]. Therefore, numerous countries have implemented the necessary infrastructure for drinking water supply, leaving rural communities to take responsibility for its operation and maintenance [2].

Rural drinking water systems (hereinafter RDWs) are supplied by collecting surface or groundwater. The purity and physicochemical quality of these water sources depend on the hydrological and hydrogeological conditions of the basin [3], as well as the human activities carried out on the surface that diffusely contaminate the water resource [4]. In addition, in recent decades, the effects of climate change on the recharge regime of watercourses and aquifers have had an impact on the availability and quality of the resources, both from surface and underground sources [5]. In the case of underground sources, the reduction in groundwater flows and levels due to geological or anthropogenic causes has led to a gradual increase in the concentrations of some pollutants present in soils.

Among rural anthropogenic processes, the percolation of fertilizers, pesticides and slurry derived from agricultural activity constitutes a potential risk to the health of communities that use water sources. It should be considered that the global agricultural industry has increased the incorporation of pesticides, nitrogen, and phosphate fertilizers, generating a greater accumulation of these allochthonous elements in aquifers. In particular, it is estimated that only 1% of the pesticides applied to crops fulfill their pest control function, whereas the other part is distributed through air, soil, surface and groundwater [6]. On the other hand, the disposal of slurry increases the concentration of microorganisms in surface water, in some cases exceeding the maximum limits established under current environmental regulations [7].

Furthermore, natural processes that influence groundwater quality in rural areas are mainly related to the types of rocks, soil erosion and leaching processes [8], and biological processes in the aquatic environment that produce changes in pH and alkalinity [9]. Specifically, the endogenous release of adsorbed manganese and iron in soils and sediments is related to low dissolved oxygen concentrations in deep water and sediments. The low O₂ concentration in the pore matrix (reductive environment) causes a reductive dissolution of both metals (FeO (OH) and MnO₂) [10]. Although these trace metals are essential for life in low concentrations, they can be detrimental to health when found in high concentrations [11].

In southern Chile, the change in land use has been an extensive process in both temporal and spatial terms and has mainly involved the replacement of native forests with areas destined for agricultural crops, grazing, forest plantations and urban development, among others [12]. From 1960 to the present, the regional replacement of native forests by forest monocultures increased to approximately 400 thousand hectares, a situation that has meant the consequent loss of goods and services associated with native forests, as in the case of water resources. Specifically in the province of Osorno, the development of the livestock sector has caused significant modifications in land use during the last century [13]; the greatest concentration of this activity is located in the medium sectors of the intermediate depression, with great development in the Osorno, Río Negro, San Pablo and Puyehue municipalities. Livestock production has improved in recent decades due to the management and improvement of pastures and the application of nitrogen and phosphorus fertilizers (increasing the amount of nutrients applied per hectare), which has allowed producers to increase the animal load [14]. Considering that the quality of drinking water in rural areas plays a fundamental role in the health and sustainability of local communities, the effect of natural processes and human influences on the quality of groundwater and surface water consumed by rural communities in southern Chile was investigated. Understanding these influences is crucial for developing effective management strategies to ensure safe drinking water, which is a fundamental human right and a critical component of public health. The underlying hypothesis is related to the influence of land use and geology in a longitudinal gradient, evaluating water quality in mountain range sectors and the intermediate depression, where different uses and soil types coexist.

2. Materials and Methods

2.1. Study Area

This study was carried out in the province of Osorno. This province extends from the Andes to the Pacific at the beginning of the southern hydrometeorological macroregion [15]; the climate in this macroregion has an average of 2963 mm of annual precipitation over an extended rainy season. Land use in the study area is divided into six general categories, with a predominance of native forests and grasslands/shrublands [16]. The areas with great development of shrublands and grasslands are located in the intermediate depression of the province, whereas the native forest is more important on the slopes of the Coastal and Andean Mountain ranges. Forest plantations are developed mainly in the eastern sector of the Coastal Mountain Range, coexisting with fragments of native forest, especially of the Valdivian rainforest type. The highest proportion of land use in the province is represented by the different sub-associations including the scrubland and grasslands, which cover 409,287 ha (49% of the total), followed by native forest (adult, renew, scrubby), with 379,406 ha (45%).

A total of six RDW systems were selected in the province of Osorno. RDWs 1 and 6 were located in areas with a predominance of native forests, while systems 2, 3, 4 and 5 were located in areas of the intermediate depression, with a predominance of agricultural and livestock grasslands (Figure 1). Four samples were obtained from boreholes (groundwaters) and were located (i) on the slopes of the mountain range of the Andes (sampling site 1), where volcanic rocks and ashes predominate; (ii) in the intermediate depression (sampling sites 2 and 3), characterized by the presence of sedimentary and volcanic rocks [17]; and (iii) on the east side of the coastal mountains (sampling site 4), where volcanic rock is also the parent material. The extraction depth of these boreholes was 70 m or more. Another two water samples corresponded to surface water (river) and were located in the coastal mountain range (sampling sites 5 and 6), characterized by the presence of metamorphic rocks and some isolated sedimentary sequences.

Soil samples were collected from the upper 0–25 cm depth in each water catchment point (sampling sites 1 to 4) or adjacent the surface water (sampling sites 5 and 6). Three samples were taken from each point (triplicated), separated by 2 m each in a linear transect. Samples were taken to the laboratory where they were dried at 35°C, homogenized and sieved to <2 mm before chemical analysis. Based on USDA classification, three samples (1 to 3) corresponded to Andisols (loam to silty loam) derived from volcanic ash and one sample (4) was classified as Ultisol (clay loam) derived from old volcanic ash; the soils of two sampling points adjacent surface water was classified as Inceptisols (silty loam to silty clay loam) derived from a mixture of sedimentary marine and volcanic ash materials (5) and from the weathering of metamorphic rock (6). All samples were also analyzed for pH (1:2.5 soil-to-water ratio) and organic matter content following the Walkey–Black method [18]. The soil characterization is shown in

Table 1. Results of pH, percentages of organic matter, iron and manganese concentrations measured in superficial soils (<25 cm) from the six rural drinking water systems of the province of Osorno. Soil classification (USDA) and texture are included [19].

Samplings Sites	Water Type	USDA Classification	Texture	pH	Organic Matter (%)	Fe (%)	Mn (mg/kg)
1	Groundwater	Typic Hapludands	Silty loam	6.20	9.5	1.54	255
2	Groundwater	Pachic Melanudands	Loam to silty loam	6.14	16.8	3.82	898
3	Groundwater	Typic Hapludands	Silty loam	5.18	15.7	4.39	1428
4	Groundwater	Typic Hapludults	Clay loam	6.20	3.6	3.33	728
5	River	Andic Dystrudepts	Loam to silty loam	5.16	3.0	3.61	873
6	River	Oxic Dystrudepts	Silty loam to silty clay loam	6.20	3.6	4.08	413

.

2.2. Determination of Physical, Chemical and Microbiological Parameters of Drinking Water

The regulations in the country regarding the drinking water quality requirements are applicable to the entire national territory [20]. Drinking water must meet the microbiological, turbidity, chemical, organoleptic and disinfection requirements described in Chilean regulations [21] to ensure its safety and suitability for human consumption.

In each RDM system, two samples of catchment water (natural or untreated water source) and one of drinking water (treated water) were obtained to determine the concentrations of the most frequent contamination parameters in the catchment sources of the rural drinking water services [20]. The research team collected these samples during two contrasting sampling seasons: one during the summer of 2019–2020 and another during the winter of 2020. Laboratory methods used for the analysis of the analytes are described in Supplementary Materials (Table S1).

There is sufficient historical and statistical background to establish the most frequent contamination parameters in the sources of rural drinking water services in Chile (20). The physical, chemical and microbiological analyses of the water samples were carried out according to the methodologies indicated in the Chilean Potability Standard.

2.3. Metals in Soil Samples

The soil samples were digested in an aqua regia mixture (concentrated HNO₃:HCl = 1:3 v/v). A modification of the ISO norm 11466 [22] was adopted. Two grams (2 g) of dry soil previously grounded to pass a 0.5 mm sieve was placed in a 125 mL Erlenmeyer flask with a reflux system. The acid mixture was carefully added and then the temperature was raised and maintained at 60° for 16 h with a hot plate. After that, the T° was raised to 130 °C, evaporating the mixture but avoiding total dryness. Once samples were cooled down, 5 mL of 2% HNO₃ was added and the samples were allowed to stand at 60 °C for 2 h. Finally, cooled samples were filtered into a volumetric flask and their volume was made up to 100 mL. The analyses of iron and manganese were performed in AAS equipment (5 measurements for each sample). At least 3 blanks were used in each bath of extraction and analysis.

As a quality test, a standard reference material from the National Institute of Science and Technology was digested following the same procedure (NIST 2711a, Montana soil II). This was performed to obtain an estimation of the recovery from the aqua regia digestion procedure in relation to the total metal content as certified. Average recoveries were 87% and 93% for Mn and Fe, respectively.

2.4. Statistical Analysis

Significant differences in the concentration of physicochemical and microbiological analytes between sampling sites (factor 1: sites 1 to 6) and climatic seasons (factor 2: summer and winter) were analyzed with two-way ANOVA generalized linear models (reject probability < 0.05). For the metals iron and manganese, simple linear regressions were used to estimate significant positive or negative relationships of their concentrations between soil samples and the water samples (groundwater and surface). All parametric analyses were carried out considering the statistical assumptions of normality and homoscedasticity of variances, transforming the data when they could not comply with these [23].

3. Results

3.1. Physicochemical and Microbiological Quality of Drinking Water (Treated Water) in Rural Areas of Southern Chile

The aim of treating water extracted from boreholes or surface water is to eliminate all suspended or dissolved matter that may affect the taste of the water or the health of people. At sampling sites 1, 2, 3 and 6, the concentrations of all the physicochemical and microbiological parameters measured in the drinking water samples were lower than the limits described in the Chilean drinking standard [21]. This result shows that water quality in these sampling sites is suitable for human consumption, not jeopardizing the health of the people who consume it. However, at sites 4 and 5, some values higher than the regulated ones were recorded. Specifically, turbidity exceeded the regulatory limit during summer and color was slightly higher in summer and winter at sampling site 5 (

Table 2. Analytes evaluated in drinking water samples from the selected RDWs. The selection criteria for the analytes correspond to what is indicated by Chilean regulations [20] for the rural sector, whose limit values are described in NCh 409 [21].

Analytes	Limits NCh 409	Sampling Sites
		1		2		3		4		5		6
		Summer	Winter	Summer	Winter	Summer	Winter	Summer	Winter	Summer	Winter	Summer	Winter
Turbidity	≤5 NTU	2	2	1	1	1	1	6	3	12	2	2	2
Color	≤20 units Pt-Co	8	7	1	4	2	2	11	13	21	24	10	13
pH	6.0–8.5 rank	7.04	7.06	7.68	7.63	7.82	7.73	7.66	7.54	7.44	6.91	6.58	6.67
Iron	≤0.3 mg/L	0.32	0.21	0.13	0.05	0.11	0.05	0.08	0.05	0.5	0.4	0.12	0.05
Manganese	≤0.1 mg/L	0.12	0.06	0.05	0.05	0.03	0.05	0.16	0.76	0.16	0.15	0.04	0.05
Nitratos	≤50 mg/L	0.01	0.06	0.01	0.00	0.01	0.00	0.03	0.00	0.01	0.00	0.01	0.00
Ammonium	≤1.5 mg/L	0.01	0.02	0.01	0.02	0.03	0.02	1.8	0.23	0.03	0.02	0.08	0.02
Chloride	≤400 mg/L	4.25	6.38	4.96	2.13	6.38	4.25	27.65	25.53	6.38	5.67	7.09	8.51
Total dissolved solids	≤1500	157	113	99	162	137	139	326	327	138	77	55	48
Total coliforms	<1.8 NMP/100 mL	2	2	2	2	2	2	2	2	<1.8	2	<1.8	2
Escherichia coli	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent	Absent

). The water obtained for human consumption at sampling site 5 corresponded to river water. The river presents increases in turbidity, which can be linked to the entry of sediments from coastal areas and increases in flow [24]. Visible turbidity reduces the acceptability of drinking water [1], and, although most particles that contribute to turbidity are of no health significance, many consumers associate turbidity with safety and consider murky water unsafe to drink. Changes in the color of water are correlated with increases in turbidity since the particles that are incorporated into the water column correspond to colored organic matter (mainly humic and fulvic acids), which are ubiquitous in natural waters [24]. At the same site (5), iron was slightly high, causing an increase in color. The presence of iron has a great influence on the color of water. Ideally, water for human use and consumption should not have any visible color [1]. The recorded concentrations for iron were slightly higher than the thresholds indicated in the Chilean regulations at sampling site 5, and the same was observed for manganese at sampling sites 4 and 5, with increases in winter (Table 2). Iron and manganese are metals normally present under anaerobic conditions in groundwater [10]. Furthermore, increases in iron and manganese concentrations in river waters are related to the leaching of these minerals from the surrounding soil and rocks, especially in areas with soils rich in these elements [3].

Although they were specific cases, the record of higher concentrations of iron and manganese in some sites shows that groundwater and surface water sources are susceptible to chemical contamination linked to the geological characteristics of the soils.

The hypothesis of contamination of natural origin for the aforementioned cases is reinforced when considering that these sites are located in foothills and valleys near the Coastal Mountain Range, where there are stratified deposits of volcanic–sedimentary origin, which are important sources of iron and manganese [25]. To lower the concentration of manganese and iron in the catchment waters, the drinking water communities use traditional technologies, such as filtration in mixed granular media (anthracite—green sand plus) with the addition of sodium hypochlorite and/or potassium permanganate, whose efficiency is 90–100% [20].

In drinking water samples, concentrations higher than those in the Chilean regulations were recorded for iron at sampling site 5 (0.5 mg/L in summer and 0.4 mg/L in winter) and manganese at sampling site 4 (0.76 mg/L in winter) and sampling site 5 (0.16 mg/L in summer) (Table 2). Although these concentrations are slightly higher than recommended, this water would not put the health of the people who consume it at risk. In this regard, the WHO [1] in its Water Quality Guide for Human Consumption, indicates, based on the effects on health, that it would be advisable to consume water with a concentration of less than 0.4 mg/L. Regarding iron, the WHO itself proposes no reference values based on the effects on health (see section 10), although it points out that 2 mg/L cannot imply a direct risk, and lower concentrations could affect the taste and appearance of drinking water. According to the WHO [1], excess and deficiency of metals such as iron and manganese are harmful to health, although their presence in adequate quantities is essential in the diet [11]. At levels above 0.3 mg/L, iron stains laundry and plumbing fixtures. There is usually no noticeable taste with iron concentrations below 0.3 mg/L, although turbidity and color may develop.

Analyses of the water samples from the present study indicated that in five of the six RDW systems evaluated, the nitrates and ammonium had low concentrations. However, an exceptional record was noted at sampling site 4, where the drinking water presented concentrations of ammonium (1.8 mg/L in summer) that slightly exceeded the maximum limit (1.5 mg/L) indicated in the Chilean regulations for drinking water [21]. However, this increase in ammonium would not have a negative impact on the health of consumers [1]. This slight contamination was related to the presence of domestic animals in the area. Increases in nitrates and ammonium could be attributed to nitrogen from the application of fertilizers or slurry in the drinking water samples. More complex situations have been previously recorded in southern Chile; for example, in the commune of Parral, a high concentration of nitrogen was reported in the waterwheels that was related to local livestock activities [26]. It should be noted that the quality of well waters depends on human activities carried out on the surface [4].

No fecal coliforms or Escherichia coli were recorded in the drinking water samples from the six sampling sites (Table 2). This indicates that the managers of these RDW are effectively carrying out the purification process, showing that these organizations have truly internalized its importance [2]. It is considered that low levels of total coliforms are a good indicator of the absence of pathogenic microorganisms, while waters highly contaminated with enteric bacteria could be a potential source of contagion for humans and livestock due to the presence of microorganism pathogens (i.e., Salmonella, Shigella, Vibrio, hepatitis A and E viruses, Entamoeba) capable of causing diseases through drinking water [27]. The presence of microbiological parameters may be associated with the greater exposure of surface waters, entry of organic matter, excrement and wastewater from agricultural use [27].

At the national level, some studies indicate problems in the physicochemical system and microbiological quality of water sources in rural areas. Towards the south, in the locality of Valdivia, a high concentration of microorganisms was reported in surface waters, in some cases exceeding the maximum limits established according to current environmental regulations [27]. Furthermore, in Chile, contamination from wastewater infiltration is a major problem in rural areas, where there are no comprehensive sanitation solutions, a situation that forces the use of cesspools, inadequate accumulations of garbage and, many times, the consumption of inadequately purified water [7].

Because pathogenic microorganisms are present in different concentrations in all sources of intake, drinking water treatment plants must always include, at the end, a disinfection step for the treated water. The technologies for this include dosing systems for the chlorination of treated water through the use of chlorine salt solutions [1].

3.2. Physicochemical and Microbiological Quality of Raw Water (Groundwater and Surface Water) in Rural Areas of Southern Chile

3.2.1. Anthropic Influence on the Quality of Surface Waters

Chemical and physical contaminants are usually found in surface sources as suspended or colloidal matter, whereas, in groundwater, they are found in the dissolved phase. The results indicate that turbidity, color, pH, total dissolved solids and fecal coliforms showed significant differences between groundwater and river samples (Figure 2) (ANOVA) for each variable and factor in Table S2). Specifically, higher values of turbidity (F = 8.0, p = 0.01), color (F = 5.6, p = 0.03), total dissolved solids (F = 6.0, p = 0.02) and fecal coliforms (F = 6.9, p = 0.02) were recorded, with a significantly more alkaline pH (F = 22.5, p = 0.0001) in the river waters. The color was significantly greater in the winter season (F = 7.0, p = 0.02). The remaining variables did not present significant differences between sample types or climatic seasons.

These results were expected, considering that surface water is exposed to natural and anthropogenic disturbances [28,29] and hydrological events, such as flow changes, which affect the transport and sedimentation of materials suspended in the water column and the entry of materials from the surrounding coastal areas [24] that would influence changes in color, turbidity and pH, depending on the nature of the dissolved and particulate substances transported by the river. Additionally, surface water compared to groundwater is more susceptible to contamination by sewage and animal manure, which cause increases in fecal coliforms [30].

3.2.2. Influence of Geological Factors on the Quality of Groundwaters

No microbiological agents were recorded in water from RDW systems that extract groundwater. However, these sampling sites showed significant differences in concentrations of color, iron, manganese and total dissolved solids (ANOVA) for each variable and factor in Table S2) (Figure 2). Regardless of the climatic season, manganese and total dissolved solids were higher at sampling site 4 (Mn F = 12.8, p = 0.002; TDS F = 6.8, p = 0.01) (Figure 2). Iron had a significantly higher concentration at site 1 (F = 4.3, p = 0.04). The concentrations of turbidity, nitrate, ammonium and fecal coliforms did not show significant differences between sites or climatic seasons.

Previous studies have indicated that the growing exploitation of Chilean groundwater sources reveals a problem of natural chemical contamination of the waters, a product of the geological characteristics of the soils in various areas of the country, which has also led to the need to introduce technologies for the removal of iron and manganese [20]. Both iron and manganese are naturally present in groundwater sources, and, normally, both metals are present together, with iron concentrations usually higher than manganese [20]. Specifically, iron is one of the most abundant metals on Earth, being present in natural fresh waters in concentrations of 0.5 to 50 mg/L [1].

The total contents of iron and manganese (as oxide equivalents) were in the range reported for surface samples of Chilean volcanic soils [31,32]. At the six sampling sites, the average concentration of iron in the soil varied between 15,408 mg/Kg (site 1) and 43,926 mg/Kg (site 3), while manganese had a lower concentration, varying between 255 mg/Kg (site 1) and 1428 mg/Kg (site 3). Figure 3 shows the average concentrations of both metals in the soil of each study site, along with the averages recorded in their respective water samples. The simple regression analysis indicated that the concentration of iron in soil affected its concentration in water (F = 8.2, df = 1, p = 0.01) and that 44% of the variability of this metal in water was negatively related to the increase in soil (Figure 4). On the contrary, although a positive association was observed between the concentration of manganese in water and soil, this was not significant and explained only 4% of the variability of this metal in water (F = 0.4, df = 1, p = 0.5, Figure 4).

Soil characteristics may exert marked influences on the solubility and mobility of both metals in the soil as well as charges into the soil solution and water bodies with the soil profile. The solubility of iron and manganese is controlled by pH and redox conditions. When the pH is high or redox conditions are more anoxic, the metals are transformed into more soluble forms, thus increasing the potential of their migration into the groundwater. Moreover, a reduction in the environment promotes the reductive dissolution of iron and manganese soil oxides, mobilizing these metals from the soils [33,34], potentially lowering its concentrations in that matrix during soil formation processes and increasing their concentration in ground water.

Regarding soil type, a definable trend of iron and manganese concentration in water samples was not observed. Soil type may affect metal concentrations in groundwater because of its different metal and organic matter content and mineralogy [35]. In the present study, the pseudo-total metal content was determined, but the redox properties of iron and manganese oxides of volcanic soils vary according to the type of oxide [36]. At sampling site 1 (Andisol) the iron water concentration was the highest, and at sampling site 4 (Ultisol), the water manganese concentration was the highest. High organic matter content has been associated with higher levels of iron and manganese, as a result of its redox properties, which enhance biotic reduction, increasing mobility [35,37]. In addition, the Ultisol is characterized by a higher clay content. Clay soils display a limited flow of oxygen due to the reduced size of the pore space. Thus, it becomes easy to generate in clayed soils an anoxic environment favoring the reduction and solubility of manganese (and iron). In such conditions, groundwater bodies underlying clay strata present elevated manganese concentrations [10]. Rainfall during winter may reduce soil air-filled pore space given the higher water infiltration and/or rise of the groundwater table. In our study, in the winter season, the concentration of both metals in well samples tended to be higher in comparison to summer, especially at site 4 (Figure 3). Surface waters followed a different trend. Clay is also a source of Fe-Mn nodules [35]. Although soil from site 1 was not clay soil, the water sampling point was located close to a water body (Rupanco Lake). Sediment on lakes may be enriched with iron, manganese and organic particles (with reducing potential), increasing the presence of iron and manganese in groundwater [10,37]. Although there were a limited number of samples, soil location and its organic matter and clay contents may exert an influence on iron and manganese concentrations in water from deep wells.

4. Conclusions

It is possible to conclude that the water delivered by the majority of rural drinking water systems considered in this study was of good quality, meeting the standards of Chilean and international regulations. No fecal coliforms or Escherichia coli were recorded in the drinking water samples from the six sampling sites. However, increases in turbidity, iron and manganese concentrations in drinking water would affect the acceptability of the water from sites 4 and 5 but would not present a consumer health problem linked to iron concentrations. However, the higher manganese concentration specifically recorded at site 4 during winter (0.76 mg/L) is concerning. The WHO recommends concentrations lower than 0.4 mg/L in drinking water in accordance with the maximum manganese consumption value of 11 mg/day. The metals iron and manganese are naturally present in groundwater sources, and, normally, both metals are present together, with iron concentrations usually higher than manganese. Specifically, iron is one of the most abundant metals on Earth, being present in natural fresh waters in concentrations of 0.5 to 50 mg/L according to the WHO (1).

In addition, it was determined that the water obtained from rivers compared to the water obtained from deep wells (>70 m) had lower microbiological quality and higher turbidity values. This was due to hydrological variations, mainly the dragging of materials due to increases in flow in winter and livestock activities near the rivers. Additionally, surface water compared to groundwater was more susceptible to contamination by sewage and animal manure, which cause increases in fecal coliforms. However, after chlorination, the water arrived free of microorganisms to rural consumers.

Finally, it is possible to point out that the highest concentrations of iron and manganese were recorded in raw water (untreated) from wells located in Andisol- and Utisol-type volcanic soils. Anoxic soil conditions enhanced by a higher content of clays and greater rainfall (winter) may favor the reduction and solubility of manganese (and iron) particulary in Utisol soil profiles, so the groundwater bodies underlying reductive soil strata present high concentrations of the metals. Although there were a limited number of samples, soil location and organic matter and clay contents may exert an influence on iron and manganese concentrations in water from deep wells. Further research is needed after evaluating a larger dataset.

This study contributes to the knowledge of the local reality of rural drinking water supply systems in southern Chile and also helps to understand the risks and threats linked to water sources in climate change scenarios, collaborating in taking preventive and mitigating actions to ensure this vital resource for humanity.