Water resources arenatural resources ofwater that are potentially useful for humans, for example as a source of drinkingwater supply orirrigation water. These resources can be eitherfreshwater from natural sources, or water produced artificially from other sources, such as fromreclaimed water (wastewater) ordesalinated water (seawater). 97% of the water on Earth issalt water and only three percent isfresh water; slightly over two-thirds of this is frozen inglaciers andpolarice caps.[2] The remaining unfrozen freshwater is found mainly as groundwater, with only a small fraction present above ground or in the air.[3] Natural sources offresh water includefrozen water,groundwater,surface water, and under river flow. People use water resources foragricultural,household, andindustrial activities.
Water resources are under threat from multiple issues. There iswater scarcity,water pollution,water conflict andclimate change. Fresh water is in principle arenewable resource. However, the world's supply ofgroundwater is steadily decreasing. Groundwater depletion (oroverdrafting) is occurring for example in Asia, South America and North America.
Natural sources offresh water includesurface water, under river flow,groundwater andfrozen water.
Surface water is water in a river,lake or fresh waterwetland. Surface water is naturally replenished byprecipitation and naturally lost through discharge to theoceans,evaporation,evapotranspiration andgroundwater recharge. The only natural input to any surface water system is precipitation within itswatershed. The total quantity of water in that system at any given time is also dependent on many other factors. These factors include storage capacity in lakes, wetlands and artificialreservoirs, the permeability of thesoil beneath these storage bodies, therunoff characteristics of the land in the watershed, the timing of the precipitation and local evaporation rates. All of these factors also affect the proportions of water loss.
Humans often increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans often increase runoff quantities and velocities by paving areas and channelizing the stream flow.
Natural surface water can be augmented by importing surface water from another watershed through acanal orpipeline.
Brazil is estimated to have the largest supply of fresh water in the world, followed byRussia andCanada.[4]
Glacier runoff is considered to be surface water. The Himalayas, which are often called "The Roof of the World", contain some of the most extensive and rough high altitude areas on Earth as well as the greatest area of glaciers and permafrost outside of the poles. Ten of Asia's largest rivers flow from there, and more than a billion people's livelihoods depend on them. To complicate matters, temperatures there are rising more rapidly than the global average. In Nepal, the temperature has risen by 0.6 degrees Celsius over the last decade, whereas globally, the Earth has warmed approximately 0.7 degrees Celsius over the last hundred years.[5]
Groundwater is thewater present beneathEarth's surface in rock andsoil pore spaces and in thefractures ofrock formations. About 30 percent of all readily availablefresh water in the world is groundwater.[6] A unit of rock or an unconsolidated deposit is called anaquifer when it can yield a usable quantity of water. The depth at whichsoil pore spaces orfractures and voids in rock become completely saturated with water is called thewater table. Groundwater isrecharged from the surface; it may discharge from the surface naturally atsprings andseeps, and can formoases orwetlands. Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extractionwells. The study of the distribution and movement of groundwater ishydrogeology, also called groundwaterhydrology.
Typically, groundwater is thought of as water flowing through shallow aquifers, but, in the technical sense, it can also containsoil moisture,permafrost (frozen soil), immobile water in very low permeabilitybedrock, and deepgeothermal oroil formation water. Groundwater is hypothesized to providelubrication that can possibly influence the movement offaults. It is likely that much ofEarth's subsurface contains some water, which may be mixed with other fluids in some instances.Throughout the course of a river, the total volume of water transported downstream will often be a combination of the visible free water flow together with a substantial contribution flowing through rocks and sediments that underlie the river and its floodplain called thehyporheic zone. For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow. The hyporheic zone often forms a dynamic interface between surface water and groundwater from aquifers, exchanging flow between rivers and aquifers that may be fully charged or depleted. This is especially significant inkarst areas where pot-holes and underground rivers are common.
There are several artificial sources of fresh water. One istreated wastewater (reclaimed water). Another isatmospheric water generators.[7][8][9]Desalinated seawater is another important source. It is important to consider the economic and environmental side effects of these technologies.[10]
Water reclamation is the process of convertingmunicipal wastewater or sewage andindustrial wastewater into water that can bereused for a variety of purposes. It is also called wastewater reuse, water reuse or water recycling. There are many types of reuse. It is possible to reuse water in this way in cities or for irrigation in agriculture. Other types of reuse are environmental reuse, industrial reuse, and reuse for drinking water, whether planned or not. Reuse may includeirrigation of gardens and agricultural fields or replenishingsurface water andgroundwater. This latter is also known asgroundwater recharge. Reused water also serve various needs in residences such astoilet flushing, businesses, and industry. It is possible to treat wastewater to reachdrinking water standards. Injecting reclaimed water into the water supply distribution system is known as direct potable reuse. Drinking reclaimed water is not typical.[11] Reusing treated municipal wastewater for irrigation is a long-established practice. This is especially so inarid countries. Reusing wastewater as part of sustainablewater management allows water to remain an alternative water source for human activities. This can reducescarcity. It also eases pressures on groundwater and other natural water bodies.[12]
There are several technologies used to treat wastewater for reuse. A combination of these technologies can meet strict treatment standards and make sure that the processed water is hygienically safe, meaning free frompathogens. The following are some of the typical technologies:Ozonation,ultrafiltration,aerobic treatment (membrane bioreactor),forward osmosis,reverse osmosis, andadvanced oxidation,[13] oractivated carbon.[14] Some water-demanding activities do not require high grade water. In this case, wastewater can be reused with little or no treatment.Desalination is a process that removes mineral components fromsaline water. More generally, desalination is the removal of salts and minerals from a substance.[15] One example issoil desalination. This is important for agriculture. It is possible to desalinate saltwater, especiallysea water, to produce water for human consumption or irrigation, producingbrine as a by-product.[16] Many seagoing ships andsubmarines use desalination. Modern interest in desalination mostly focuses on cost-effective provision offresh water for human use. Along with recycledwastewater, it is one of the few water resources independent of rainfall.[17]
Due to its energy consumption, desalinating sea water is generally more costly than fresh water fromsurface water orgroundwater,water recycling andwater conservation; however, these alternatives are not always available and depletion of reserves is a critical problem worldwide.[18][19][20] Desalination processes are using either thermal methods (in the case ofdistillation) or membrane-based methods (e.g. in the case ofreverse osmosis).[21][22]: 24
Researchers proposed air capture over oceans which would "significantly increasing freshwater through thecapture of humid air over oceans" to address present and, especially, future water scarcity/insecurity.[24][23]
A 2021 study proposed hypothetical portable solar-poweredatmospheric water harvesting devices. However, suchoff-the-grid generation may sometimes "undermine efforts to developpermanent piped infrastructure" among other problems.[25][26][27]
The total quantity of water available at any given time is an important consideration. Some human water users have an intermittent need for water. For example, manyfarms require large quantities of water in the spring, and no water at all in the winter. Other users have a continuous need for water, such as apower plant that requires water for cooling. Over the long term the average rate of precipitation within a watershed is the upper bound for average consumption of natural surface water from that watershed.
Irrigation is the practice of applying controlled amounts ofwater toland to help growcrops,landscape plants, andlawns. Irrigation has been a key aspect ofagriculture for over 5,000 years and has been developed by many cultures around the world. Irrigation helps to grow crops, maintain landscapes, andrevegetate disturbed soils in dry areas and during times of below-average rainfall. In addition to these uses, irrigation is also employed to protect crops fromfrost,[28] suppressweed growth ingrain fields, and preventsoil consolidation. It is also used to coollivestock, reducedust, dispose ofsewage, and supportmining operations.Drainage, which involves the removal of surface and sub-surface water from a given location, is often studied in conjunction with irrigation.
Several methods of irrigation differ in how water is supplied to plants.Surface irrigation, also known as gravity irrigation, is the oldest form of irrigation and has been in use for thousands of years. Insprinkler irrigation, water is piped to one or more central locations within the field and distributed by overhead high-pressure water devices.Micro-irrigation is a system that distributes water under low pressure through a piped network and applies it as a small discharge to each plant. Micro-irrigation uses less pressure and water-flow than sprinkler irrigation.Drip irrigation delivers water directly to the root zone of plants.Subirrigation has been used in field crops in areas with high water tables for many years. It involves artificially raising the water table to moisten the soil below the root zone of plants.It is estimated that 22% of worldwide water is used inindustry.[29] Major industrial users includehydroelectric dams,thermoelectric power plants, which use water forcooling,ore andoil refineries, which use water inchemical processes, and manufacturing plants, which use water as asolvent. Water withdrawal can be very high for certain industries, but consumption is generally much lower than that of agriculture.
Water is used inrenewable power generation.Hydroelectric power derives energy from the force of water flowing downhill, driving a turbine connected to a generator. Thishydroelectricity is a low-cost, non-polluting, renewable energy source. Significantly, hydroelectric power can also be used forload following unlike most renewable energy sources which areintermittent. Ultimately, the energy in a hydroelectric power plant is supplied by the sun. Heat from the sun evaporates water, which condenses as rain in higher altitudes and flows downhill.Pumped-storage hydroelectric plants also exist, which use grid electricity to pump water uphill when demand is low, and use the stored water to produce electricity when demand is high.
Thermoelectric power plants usingcooling towers have high consumption, nearly equal to their withdrawal, as most of the withdrawn water is evaporated as part of the cooling process. The withdrawal, however, is lower than inonce-through cooling systems.
Water is also used in many large scale industrial processes, such as thermoelectric power production, oil refining,fertilizer production and otherchemical plant use, andnatural gas extraction fromshale rock. Discharge of untreated water from industrial uses ispollution. Pollution includes discharged solutes and increased water temperature (thermal pollution).
It is estimated that 8% of worldwide water use is for domestic purposes.[29] These includedrinking water,bathing,cooking,toilet flushing, cleaning, laundry andgardening. Basic domestic water requirements have been estimated byPeter Gleick at around 50 liters per person per day, excluding water for gardens.
Drinking water is water that is of sufficiently high quality so that it can be consumed or used without risk of immediate or long term harm. Such water is commonly called potable water. In most developed countries, the water supplied to domestic, commerce and industry is all of drinking water standard even though only a very small proportion is actually consumed or used in food preparation.
844 million people still lacked even a basic drinking water service in 2017.[30]: 3 Of those, 159 million people worldwide drink water directly from surface water sources, such as lakes and streams.[30]: 3 One in eight people in the world do not have access to safe water.[31][32] Unsafe drinking water leads to 1.2 million deaths per year according to the World Bank.[33]
The world's supply ofgroundwater is steadily decreasing. Groundwater depletion (oroverdrafting) is occurring for example in Asia, South America and North America. It is still unclear how much natural renewalbalances this usage, and whetherecosystems are threatened.[50]
Water resource management is the activity of planning, developing, distributing and managing the optimum use of water resources. It is an aspect ofwater cycle management. The field of water resources management will have to continue to adapt to the current and future issues facing the allocation of water. With the growing uncertainties of globalclimate change and the long-term impacts of past management actions, this decision-making will be even more difficult. It is likely that ongoing climate change will lead to situations that have not been encountered. As a result, alternative management strategies, including participatory approaches andadaptive capacity are increasingly being used to strengthen water decision-making.
Ideally, water resource management planning has regard to all the competingdemands for water and seeks to allocate water on an equitable basis to satisfy all uses and demands. As with otherresource management, this is rarely possible in practice so decision-makers must prioritise issues of sustainability, equity and factor optimisation (in that order!) to achieve acceptable outcomes. One of the biggest concerns for water-based resources in the future is thesustainability of the current and future water resource allocation.
Sustainable Development Goal 6 has a target related to water resources management: "Target 6.5: By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate."[52][53]
At present, only about 0.08 percent of all the world's fresh water is accessible. And there is ever-increasing demand fordrinking,manufacturing,leisure andagriculture. Due to the small percentage of water available, optimizing the fresh water we have left fromnatural resources has been a growing challenge around the world.
Much effort in water resource management is directed at optimizing theuse of water and in minimizing theenvironmental impact of water use on the natural environment. The observation of water as an integral part of theecosystem is based onintegrated water resources management, based on the 1992Dublin Principles (see below).
Sustainable water management requires a holistic approach based on the principles ofIntegrated Water Resource Management, originally articulated in 1992 at the Dublin (January) and Rio (July) conferences. The four Dublin Principles, promulgated in theDublin Statement are:
Implementation of these principles has guided reform of national water management law around the world since 1992.
Further challenges to sustainable and equitable water resources management include the fact that many water bodies are shared across boundaries which may be international (seewater conflict) or intra-national (seeMurray-Darling basin).
Integrated water resources management (IWRM) has been defined by theGlobal Water Partnership (GWP) as "a process which promotes the coordinateddevelopment and management of water, land and related resources, in order to maximize the resultanteconomic andsocial welfare in an equitable manner without compromising thesustainability of vitalecosystems".[54]
Some scholars say that IWRM is complementary towater security because water security is a goal or destination, whilst IWRM is the process necessary to achieve that goal.[55]
IWRM is a paradigm that emerged at international conferences in the late 1900s and early 2000s, although participatory water management institutions have existed for centuries.[56] Discussions on a holistic way of managing water resources began already in the 1950s leading up to the 1977 United Nations Water Conference.[57] The development of IWRM was particularly recommended in the final statement of the ministers at the International Conference on Water and the Environment in 1992, known as theDublin Statement. This concept aims to promote changes in practices which are considered fundamental to improvedwater resource management. IWRM was a topic ofthe second World Water Forum, which was attended by a more varied group of stakeholders than the preceding conferences and contributed to the creation of the GWP.[56]
In theInternational Water Association definition, IWRM rests upon three principles that together act as the overall framework:[58]
In 2002, the development of IWRM was discussed atthe World Summit on Sustainable Development held in Johannesburg, which aimed to encourage the implementation of IWRM at a global level.[59]The third World Water Forum recommended IWRM and discussed information sharing, stakeholder participation, and gender and class dynamics.[56]
Operationally, IWRM approaches involve applying knowledge from various disciplines as well as the insights from diverse stakeholders to devise and implement efficient, equitable and sustainable solutions to water and development problems. As such, IWRM is a comprehensive,participatory planning and implementation tool for managing and developing water resources in a way that balances social and economic needs, and that ensures theprotection of ecosystems for future generations. In addition, in light of contributing the achievement ofSustainable Development goals (SDGs),[60] IWRM has been evolving into more sustainable approach as it considers the Nexus approach, which is a cross-sectoral water resource management. The Nexus approach is based on the recognition that "water, energy and food are closely linked through global and local water, carbon and energy cycles or chains."
An IWRM approach aims at avoiding a fragmented approach of water resources management by considering the following aspects: Enabling environment, roles of Institutions, management Instruments. Some of the cross-cutting conditions that are also important to consider when implementing IWRM are: Political will and commitment, capacity development, adequate investment,financial stability and sustainable cost recovery, monitoring and evaluation. There is not one correct administrative model. The art of IWRM lies in selecting, adjusting and applying the right mix of these tools for a given situation. IWRM practices depend on context; at the operational level, the challenge is to translate the agreed principles into concrete action.
Integrated urban water management (IUWM) is the practice of managingfreshwater,wastewater, andstorm water as components of abasin-wide management plan. It builds on existingwater supply andsanitation considerations within anurban settlement by incorporating urbanwater management within the scope of the entire river basin.[61] IUWM is commonly seen as a strategy for achieving the goals ofWater Sensitive Urban Design. IUWM seeks to change the impact ofurban development on the naturalwater cycle, based on the premise that by managing the urban water cycle as a whole; a more efficient use of resources can be achieved providing not only economic benefits but also improved social and environmental outcomes. One approach is to establish an inner, urban, water cycle loop through the implementation of reuse strategies. Developing this urban water cycle loop requires an understanding both of the natural, pre-development, water balance and the post-development water balance. Accounting for flows in the pre- and post-development systems is an important step toward limiting urban impacts on the natural water cycle.[62]
IUWM within an urban water system can also be conducted by performance assessment of any new intervention strategies by developing a holistic approach which encompasses various system elements and criteria includingsustainability type ones in which integration of water system components includingwater supply,waste water andstorm water subsystems would be advantageous.[63] Simulation ofmetabolism type flows in urban water system can also be useful for analysing processes in urban water cycle of IUWM.[63][64]Water resource management and governance is handled differently by different countries. For example, in theUnited States, theUnited States Geological Survey (USGS) and its partners monitor water resources, conduct research and inform the public about groundwater quality.[65] Water resources in specific countries are described below:
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