WATER: A FUNDAMENTAL RESOURCE FOR ENSURING SUSTAINABILITY

Objective: The objective of the study is to carry out a bibliographical review to understand the hydrological cycle and the importance of care of water for the maintenance of water resources and biodiversity in the pursuit of sustainability for present and future generations. Theoretical framework: Water is essential for human consumption, crop irrigation, animal watering, industrial production, energy generation and maintenance of biodiversity. However, water resources have been suffering anthropic pressures that affect the availability of water in quality and quantity, directly inferring sustainability. Method: This is a qualitative narrative review of the literature about the importance of water for the sustainability of life. The research was carried out through online access to Google Scholar databases, during the months of October to November 2021. Results and conclusion: The availability of water in quantity for its multiple users is not enough. The compression of relationship between water and the sustainability of life and ecosystems in general is necessary. Therefore, more than monitoring is raising awareness among the population, recognizing water as an essential element for social, economic and environmental sustainability. Originality/value: Study that relates the importance of water and the hydrological cycle for the sustainability of life, providing solid bases for knowledge and awareness of the importance of care and preservation, contextualizing from a systemic and multidisciplinary view.


INTRODUCTION
Water is an essential substance for life on the planet and a fundamental resource for the development of societies, used for diverse human activities: human consumption, irrigation of crops and gardens, livestock watering, industrial production, and generation of energy. In addition, water is essential for the maintenance and functioning of ecosystems. In this sense, water must be guaranteed in quantity and quality to meet the needs of all living beings in their ecosystems. Water availability and the ability to preserve and conserve water resources are limiting factors for the socioeconomic development of countries (Postel, 1996;Postel, 1998;Baron et al., 2002;Poff et al., 2003;Abera et al., 2011;Baker & Miller, 2013;Ferreira et al., 2017).
It is estimated that 2.5% of the world surface water is fresh and its distribution is not uniform across the globe. In addition to the limited amount of available water, the water quality required for several purposes is another worldwide concern. The lack of drinking water is among serious problems that concern world authorities. In this sense, the UN 2030 Agenda composed global actions to meet 17 Sustainable Development Goals (SDGs) ( Figure 1); SDG 6 is directly related to water. Furthermore, the United Nations General Assembly established 2018-2028 as the International Decade for Action: Water for Sustainable Development (Filho, 2018;Un, 2020;Bárta et al., 2021;Copetti et al., 2022;Baracho & Scalize, 2023). Surface waters in streams, rivers, and lakes and groundwater are characterized by instability and mobility in a constant and dynamic cycle called hydrological cycle. This dynamic can be compared to a large flow in which one of the sources is the water springs, defined as natural water outcrops, forming a watercourse. The water emergence occurs from the water table to the ground surface, where groundwater naturally accumulates, forming lakes or water courses such as streams and rivers (Brasil, 1985;Tundisi, 2003;Brasil, 2006;Brasil, 2012;Leal et al., 2017;Machado & Soares, 2018;Macedo et al., 2020).
Small streams originating from water springs form the contribution network of a hydrographic basin, which is a geographic unit consisting of a land area that contributes to the formation and storage of a watercourse. In this sense, degradation of springs can harm water course due to reductions in flow and, in extreme cases, water courses can dry up, hindering water quality and availability and affecting all living beings that depend on it to survive (Alves, 2000;Valente & Gomes 2015). Machado & Soares (2018) emphasized that everything starts with water springs, which are responsible for the entire river/water network of any watershed and are fundamental for forming and renewing water courses. In addition, these waters are often used as a source for human consumption, animal watering, and crop irrigation. Therefore, water springs are essential to maintain the quality and quantity of water of streams and rivers and ensure their continuity (Tundisi, 2008;Marmontel et al., 2018).
In this context, despite the importance of water for the maintenance of water resource, biodiversity and survival of the human species, there is a compromised in the availability of its waters, both in quantity and quality. Disorderly population growth, deficient public sanitation systems, climate change, deforestation practices with suppression of riparian forests, agricultural activities, inappropriate land use, and unplanned urbanization are among factors that potentiate the imbalance process of the hydrological cycle and the natural characteristics of water (Postel, 1998;Jackson et al., 2001;Pinto et al., 2004;Hepp & Restello, 2007;Balaji et al., 2012;IPCC, 2014;Honda & Durigan, 2017;Galvan et al., 2020;Daronco et al., 2020).
Tundisi 2003 emphasized that human actions that interfere with natural cycles and water availability, both quantity and quality, have compromised the sustainability of water resources. In this sense, the concept of water-environment sustainability, which refers to integrated management of water resources in a region, involving various aspects of water, such as the hydrological cycle; the different uses of water; the interrelationship between natural and social systems; and the interdependence between the economic, social, and environmental scopes that characterize sustainable development (Vieira, 1996;Bomfim et al., 2015).
In this context, the objective of the present research was to carry out a bibliographic review for a deep understanding the hydrological cycle and the importance of taking care of water for the maintenance of water resources and biodiversity and the guarantee of sustainability for present and future generations.

MATERIALS AND METHODS
This is a qualitative narrative review of the literature, focused on developing the state of the art on the importance of water for the sustainability of life. In this perspective, the following topics are presented: an essential resource for sustainability; legislation and management of water quality in Brazil; monitoring of water quality; hydrological cycle and formation of water resources; and surface and underground water sources. The research was carried out through online access to the Google and Google Scholar databases from October to November 2021. Scientific articles in any language, from several national and international journals, and other documents that addressed the main subject were selected and read. Considering that this is a narrative-type review, inclusion or exclusion criteria were not defined for the selection of materials used in the development of this research. This methodological configuration is described in the work developed by Rother (2007).

Water Hydrological Cycle in the Formation of water Resources
The essential characteristic of any volume of surface water in rivers, lakes, ponds, and artificial dams, and groundwater is the instability and mobility in a closed, continuous, and dynamic cycle called hydrological cycle (Figure 2), whose operation is sequential, with different elements that contribute to keeping the cycle in balance, which includes springs. In this cycle, water passes through the three physical states: solid, liquid, and gas, whether on the surface, atmosphere, and biosphere through precipitation, evapotranspiration, infiltration, and surface runoff. Water availability in the liquid phase is the most important for the human needs. The total amount of water that participates does not change, as it is a closed cycle; however, its distribution and quality in the main environments that make it available may change, even if temporarily (Shiklomanov, 2000;Tundisi, 2003;Brasil, 2006;Silva & Pereira, 2019).
Watersheds are important for the dynamics of the hydrological cycle, as they represent a surface land area that favors the formation of watercourses and contribute to water storage. They are composed of numerous springs that form small and the streams that form the drainage network. Part of the water that is precipitated in the watershed as rain is intercepted by plants, part is evaporated, part drains superficially or form runoffs which drains quickly into the basin, and part infiltrates the soil, which is responsible for feeding the aquifers that constitute the saturated layer of the soil profile (Alves, 2000;Fritzen & Binda, 2011;Valente & Gomes, 2015).
This saturated layer can be close to the surface or deep, whether under pressure. The artesian or confined layer is between impermeable layers and the water moves under pressure. The water table is characterized by the saturated region over an impermeable layer, usually a rocky substrate, without exerting pressure other than atmospheric pressure. It usually has a local formation, delimited by the contours of the hydrographic basin, originated from rainwater that infiltrates the soil through permeable layers until reaching the impermeable layer (Romero, 2017). The total amount of water that participates in the hydrological cycle does not change, as it is a closed cycle; however, its distribution and quality can be modified in the main environments that retain water, sometimes transiently (atmosphere, oceans, and continents). In this way, considering that the total amount of water does not change, care is needed to ensure that it remains in good conditions for use in the place of interest, once water is becoming increasingly inaccessible to those who need it. Thus, vegetation is fundamental for the retention of water on continents, as the amount of water that infiltrates the soil depends on it, guarantees the flows of springs and wells, and is the most responsible for the continuity of surface water bodies (Brasil, 2006;Carvalho et al., 2012;Garcia et al., 2018).

Surface and Underground Water Sources
The fresh water available for human use is in the hydrological cycle in the surface and groundwater, which characterize water resources. Surface water flows or is stored on the ground surface by the contribution of precipitation, aquifer recharge, and surface water bodies, including rivers, lakes, and runoff. They exist in great quantity, allowing for good capture conditions; however, they tend to have lower quality indices. Groundwater is that found in the subsoil or in the soil and is defined as the water that is stored inside the soil through infiltration and percolation through soil layers and rocks, generating reserves called aquifers. It is an important component of the hydrological cycle, as it constitutes part of rainfall and contributes to the hydrological balance (Almeida et. al., 2021).
Groundwater reserves are distributed throughout the Brazilian territory in different types of reservoirs, which consist of porous, fractured-karst (carbonate rocks), fractured (crystalline rocks), and fractured-volcanic aquifer domains. The Brazilian underground reserves are currently under analysis, which shows an estimated availability of 11,430 m³ s-1, much lower than the surface water availability, which is approximately 91,300 m³ s-1. They are not the solution to the water crisis, but an important source for public supply and human consumption.
Regarding surface water resources, Brazil is one of the richest countries; however, it is characterized by a high climate variability that reflects in an unequal spatial distribution of available resources. Therefore, it presents extremes, such as: i) water scarcity, with water availability below 100 m3 s-1 in the Northeast region; and ii) high water availability, reaching flows of approximately 74 thousand m3 s-1 in the Amazon Hydrographic Region (Ana, 2010). Brazil also has the largest hydrographic basin in the world, with seven million square kilometers distributed in twelve hydrographic regions. The Brazilian demand for water use is growing, with an estimated increase of approximately 80% in the total amount in the last two decades. It is estimated that water consumption will increase by 26% by 2030. This historic increase is a consequence of economic development, urbanization processes, and agriculture, which has high water demand for irrigation (Ana, 2017).
Brazilian water management systems have prioritized the use of surface water resources; however, groundwater extraction has increased in recent years. Brazil has been showing a reduction in supply from surface water since 2012, which has led the Government to search for ways to reduce consumption and restrict access to water. This strategic change occurred due to the degradation of surface water quality by the release of sewage and other contaminants on an increasing scale. In addition, the occurrence of extreme events caused by climate change has resulted in very low levels of water in reservoirs, bringing the increase in groundwater extraction to the debate (Telles & Costa, 2010;Villar, 2016).

Legislation and Water Quality Management in Brazil
Management of water resources in Brazil is focused on guaranteeing water availability and quality for diverse uses, including public supply and environmental preservation. The concern with water quality was structured through the creation of the National Water Resources Policy (PNRH) and the National Water Resources Management System (SINGREH), established by the Law 9433/97. The objectives include ensuring water availability to current and future generations, with appropriate quality standards for each use (Brasil, 1997;Ana, 2021).
The Currently, the classification of surface water bodies and guidelines for their classification are established by CONAMA Resolution no. 357/2005 (Brasil, 2005). Regarding the control of potable water for human consumption, the Annex XX of the Consolidation Ordinance no. 5/2017 (Brasil, 2017) was amended by the Ordinance GM/MS no. 888/2021 (Brasil, 2021). In the state of Rio Grande do Sul, water quality monitoring is complemented by the SES Ordinance no. 320/2014 (Rio Grande do Sul, 2014).
The CONAMA Resolution 357/2005 classifies waters in the national territory for ensuring their predominant uses, by defining levels for treatment of effluents, facilitating framing and planning for using water resources, creating means to assess the evolution of water quality to preserve human health and the aquatic ecological balance, and establishing the division of waters into fresh, brackish, and saline waters. In addition, it defines water quality as the quality condition presented by a water body at a given time, regarding possible uses with adequate safety, in view of their quality classes (Brasil, 2005).
The Annex XX of the Consolidation Ordinance no. 5/2017 defines the control and surveillance procedures for water quality for human consumption and water potability standards (Brasil, 2017). The Ordinance GM/MS no. 888/2021 amends the potability standards defined in the Annex XX of the Consolidation Ordinance GM/MS no. 5/2017 to provide control and surveillance procedures for water quality for human consumption and standards of potability (Brasil, 2017;Brasil, 2021).
The SES Ordinance no. 320/2014 establishes additional parameters to the potability standards regarding chemical substances for control and surveillance of water quality for human consumption in the state of Rio Grande do Sul. It was considered necessary to increase the number of substances monitored in Rio Grande do Sul due to its climate and edaphic characteristics and its diversified agricultural production, for which, a significant number of pesticides is used (Rio Grande do Sul, 2014).

Water Quality Monitoring
Human activities have been compromising the maintenance of quality and quantity of water due to occupation of recharge areas for economic activities; inappropriate land use practices, causing soil erosion; elimination of native vegetation in permanent preservation areas; uncontrolled population growth and an increasing urbanization with poor basic sanitation systems; and inadequate disposal of solid waste and increased impermeable areas (Tucci, 2008;Machado & Soares, 2018;Failla et al., 2021). Damage to water quality caused by human activities is one of the world's major problems and demands the development and adaptation of methods for assessing environmental quality (Prestes & Vincenci, 2019).
Environmental monitoring programs are instruments that enable the generation of standard reference situations, which essentially consist of specific measurements and observations to assess the occurrence of certain environmental impacts and measure their intensities, in addition to evaluate the effectiveness of implemented preventive measures (Forio & Goethals, 2020). Environmental monitoring of water resources is an analytical procedure that periodically assesses water quality by measuring physical, chemical, and microbiological characteristics. These parameters are widely used as indicators; their levels and concentrations are used as reference to classify water bodies into the established classes (Silva & Gasparetto, 2016;Ana, 2017).
The results obtained enabled to characterize and analyze the surface water status in hydrographic basins; subsidize planning, control, recovery, preservation, and conservation measures for the environment under study; and mainly assist in the definition of environmental policies. In this sense, environmental monitoring provides a deep understanding of the manenvironment relationship and shows the performance of institutions in conducting plans, programs, and projects, which are legal and financial tools for maintaining the environment in good conditions or for recovering degraded aquatic environments (Mayer et al., 2013;Almeida et al., 2021).
The analysis of these for monitoring water quality enables the classification of fresh waters into the classes 1, 2, 3, and 4, according to the CONAMA Resolution no. 357/2005. However, they cannot differentiate compounds that can be absorbed by the body from inert compounds, thus compromising the environmental assessment and underestimating the true impact on the aquatic biota (Karr et al., 1999;Goulart & Callisto, 2003;Isidori et al., 2003;Brasil, 2005;Rodrigues & Castro, 2008;Kieling-Rubio et al., 2015).
Considering the needs of the different water users, these parameters are also used to evaluate characteristics related to potability, according to the standards established by the Ordinances of the Ministry of Health and the State Secretary of Health. These characteristics show several processes that occur in the water body, determining the potential for quality or toxicity (Soares & Ferreira, 2017;Klamt et al., 2021;Almeida et al., 2021).
This traditional monitoring has some advantages in the assessment of environmental impacts on aquatic ecosystems, such as the immediate identification of changes in the water physical and chemical properties, and accurate detection and determination of altered concentrations. However, this practice also has disadvantages, such as: it records results from the moment the samples were collected for analysis; reveals a momentary portrait of what can be a highly dynamic situation, and generates temporal and spatial discontinuity of the samples, i.e., requires a large number of analyses to carry out an efficient temporal monitoring; has low efficiency to detect changes in habitat diversity; and is insufficient to determine the consequences of these changes for water quality in biological communities. Furthermore, when the collections are carried out at points far from the polluting source, the assessments do not detect subtle disturbances on the ecosystem (Pratt & Coler, 1976;Goulart & Callisto, 2003).
In this context, assessing environmental impacts on water quality requires a comprehensive analysis that involves physical, chemical, microbiological, and biological parameters that allow an adequate characterization for the proper management of water resources through biomonitoring. The advantages of this monitoring are low-cost, efficiency and speed in obtaining results, and a highly sensitive to changes in the habitat, even if contamination is not detected by other methods of analysis. Moreover, ecological indicators are important to assess environmental conditions over time (Hepp & Restello, 2007;Pimenta et al., 2016;Ferreira et al., 2017).
Biological monitoring or biomonitoring is performed through the application of different assessment protocols and biological and multimetric indices based on bioindicators. The main methods include the survey and evaluation of changes in species richness and diversity indices, abundance of resistant organisms, loss of sensitive species, measures of primary and secondary productivities, and sensitivity to concentrations of toxic substances (ecotoxicological assays) (Barbour et al., 1999). This method is based on changes in the structure and composition of aquatic organism communities. However, the response time of several groups of organisms in the environment can be considerably long (years to decades), thus, specific groups (protozoa, ciliates, algae, benthic macroinvertebrates, and fish) have been selected for the obtaining of immediate responses, using different analysis methods (Parmar et al., 2016;Forio & Goethals, 2020).

Water: An Essential Resource for Sustainability
Water is an indispensable resource for the continuation of life and the most important constituent on Earth, as it is required for most anthropogenic, biological, and metabolic processes. Approximately 70% of the Earth's surface is composed of fresh and salt water: approximately 97.5% are salt and 2.5% are fresh water. Regarding fresh water, 69% is found in glaciers that are not available for use; 30% is groundwater, making it difficult to use for human acquisition due to its depth or condition; and 0.9% is in other forms (soil moisture and swamps). Thus, only 0.3% of surface water remains in lakes and rivers and can be easily used for human consumption. Therefore, despite the great water availability on the planet, a low percentage can be used for the essential processes to maintain human life on Earth (FUNASA, 2014;Ana, 2021;Koch et al., 2023).
Water resources are used throughout the planet for numerous activities, including industrial and agricultural activities. According to data of the United Nations Food and Agriculture Fund, agriculture is responsible for approximately 70% of the world's water consumption, industrial processes consume 20%, and 10% is divided between domestic uses and other activities. These data show that trends in water use in the world aim to meet economic and social needs (Honda & Durigan, 2017;Boretti & Rosa, 2019).
The current water degradation is one of the most discussed and concerning issues due to the high demand, current amount available on earth, and possible scarcity and/or contamination of water, which is already a reality in some parts of the globe. Decreases in water quantity and quality are due to the lack of planning and or non-compliance with it. Considering the great increase in pollution, the environment is not been maintaining its balance due to its capacity to absorb pollutants. In this sense, environmental changes are getting so high that neutralizing and absorbing damage is no longer possible (Boretti & Rosa, 2019;Herrfahrdt-Pähle et al., 2019;Daronco et al., 2020).
Considering concerns about serious problems that threaten sustainability of life on the planet, the UN representatives launched the 2030 Agenda, composed of 17 Sustainable Development Goals (SDGs). The data presented show that the lack of water affects 40% of the world's population, and the estimate is that it will increase due to climate change and lack of effective management of aquatic environments. Water is a key factor for socioeconomic development of populations; therefore, its conscious and sustainable use is necessary to avoid scarcity and ensure availability in the future. In this context, drinking water and sanitation is one of the scopes of the SDGs, which seeks to ensure availability of water and its sustainable management (Tundisi, 2003;FAO, 2003;Un, 2020).
Brazil holds approximately 12% of the world's total fresh water and is considered the richest country in drinking water, with 53% of the fresh water in South America and 12% of the world's fresh water. However, considering that the main water sources provide 80% of the water production, a possible scarcity and water stress are expected. Thus, although Brazil has great water availability, this water is not evenly distributed among the regions: 70% of the water is in the Amazon basin, which presents the lowest population density in the country; 5% of fresh water are in the Northeast, which has 30% of the population; 12.5% is in the South and Southeast regions, which concentrate 60% of the country's population. This uneven distribution makes Brazil the twentieth in the world ranking of absolute availability of renewable water resources, even though it is the largest in water reserves on the planet (Paz et al., 2000;Fagundes et al., 2020).
The importance of water, in the biological context, is because it represents flow, movement and life, whether plant or animal in an aquatic or terrestrial environment. In water courses, in contact with the soil, oxygen, light and nutrients allow the establishment of micro and macroscopic organisms of different groups. Among these organisms, the benthic macroinvertebrates that live at the bottom of watercourses stand out, at least in one of the phases of their life cycle or throughout it. They are very important by participating in several processes in aquatic ecosystems, including nutrient cycling, energy flow, food source for fish, and releasing of nutrients into the water (Rosenberg & Resh, 1993;Queiroz et al., 2008;Hussain & Pandit, 2012;Zardo et al., 2013). Mostly, they feed on algae and microorganisms, which are the primary source of food resource. Fish and other vertebrates represent their main predators and this is how the various segments of the food chain begin (Silveira, 2004).
To assess this intense relationship, many scientific studies have been and are being developed and have shown that the reduction or increase in the diversity of these organisms is connected with the health of the ecosystem or the biological integrity of the environment in which the water is inserted and, consequently, to the land use and occupation in its surroundings. Santos and Melo 2017 concluded that the diversity of individuals decreases proportionally to the degree of land use and occupation, denoting its impact on water quality (Epa-Ohio, 1987).
With regard to plant development, water is an essential resource because it acts directly in several physiological processes, including the photochemical process of photosynthesis, in the transport and absorption of nutrients. Water represents about 90 to 95% of the green biomass of plants and is essential for the functional maintenance of tissues, cells and organisms. It is considered a predominant and restrictive requirement for plant growth, as it is the livelihood, its absence represents the death of plants due to the inability to carry out their physiological processes for maintenance in the environment (Campos, Santos & Nacarath, 2021).
For the maintenance of socio-economic development, the availability of water in quantity and quality is essential. The growing demand for food and other consumer goods has required the intensification of production processes, whether agricultural or industrial, which require water for their development. However, this intensification can compromise water sources, whether surface or underground. In the same way, the disorganized demographic expansion and a deficient sanitary system, contribute for the compromising of the quality of the water. With regard to food production, global growth has been exerting strong pressure on water resources. Expansion of irrigation systems will likely intensify depletion of waterways and aquifers, a concern about the ability to sustain human life with their finite freshwater resources (Jannuzzi et al., 2020;Soares & Signor, 2021).
However, the development of a society needs to occur in a sustainable way, with balance in the social, economic and environmental spheres, without compromising water resources. Water is essential for the life of any and all living beings, including humans, and its sustainability depends on the ability of ecosystems to meet the needs of present and future generations (Jannuzzi et al., 2020;Soares & Signor, 2021).

CONCLUSION
The understanding of the importance of water for the sustainability of life is necessary, as well as the understanding of its cycle on the planet, serving as a subsidy for the establishment of efficient plans for the protection and preservation of this renewable but finite natural resource.
The availability of water in quantity for its multiple users is not enough. In this sense, care and monitoring is fundamental, also observing the current legislation. However, more than monitoring is the awareness of the population, recognizing water as an essential element for social, economic and environmental sustainability.