Water resources are of the essentialnatural resources that are very useful in all aspects of human life, as potential resources, they can be renewed and recycled and stored over longer time. Water is used on a daily basis for different purposes such as for washing, cleaning, irrigation, swimming, cooling and manufacturing of goods both in our homes and in various industries, all living things require water to grow and reproduce. Water is a physical substance that is unique in all aspects; it can exist in all three states of matter such as solid, liquid and gaseous state and at a specific temperature found at the surface of the earth. Water is a universal solvent; it is stored in various parts of the world, starting from the atmosphere through the river channel up to ground water. Water also possesses important economic, legal and political aspects as well and it is not evenly distributed all over the surface of the earth.

Meaning of Water Resources

Water resources include all the things that have to do with water; things are derived from water bodies and are of great benefits to man and his environment. Water resources are also referred to as sources of water that are useful or potentially useful. Uses of water include for agricultural uses, generation of electricity, industrial uses, household uses, recreational uses and environmental activities.Some sources of water include, rain, sea, stream, lake, pond, bore hole and well.

Water possess important economic, legal and political aspects as well as it is not uniformly distributed all over the surface of the earth, however the knowledge of the physical distribution of water is basic to the understanding of the social, economic and political problems that surround water resources management.

Some areas of the earth are blessed with fairly uniform and more than adequate supply for human needs whereas, many other places have a greater need of water than the supply.Dry conditions in arid or semi-arid regions exist far much if not throughout the year. Water is in great demand in dry region and considerable time and efforts are expected by the people of such region in searching for it, in transporting it to regions of greatest need and in storing it for longer use. In such areas, water is quite costly and ownership of supply is something to be prized. Money and labor are required to developed available supplies of water.

Even in more humid areas economy enters into the picture for example, to purify existing water sources for a particular human and industrial purposes, or to keep polluted wastewater out of the ground water or surface water supplies requires huge sum of money. Since water is vital, for most domestic, agricultural and industrial purposes, the economy of water is an important issue in water supply management.

Different Sources of Water

1. Water in the atmosphere: water vapor in the lower atmosphere varies generally from close to 0%- 4% by volume from region to region. It has been estimated that if all the water in the atmosphere were precipitated out at one time, there would be enough to cover the surface of the globe to a depth of about 25mm multiplied by the area of the globe; this gives a total volume of water to be 13,00km³ in the atmosphere.
2. Water in the ocean: The world’s oceans, with a total volume of more than 500 million cubic kilometers, hold more than 97 percent of all the water on Earth. However, the 3.5-percent salt content of this water makes it unusable for most human needs. The extraction of fresh water from the ocean water has been carried out for many years, but provides only a very small portion of the water used and remains quite expensive relative to land-based water resources. A rough figure for the amount stored in the oceans of the world can be obtained from an estimate of the average depth of the ocean multiply by the oceans themselves. Based on the estimated the average depth of the ocean is 12,500ft (12500x 0.3050), 3810m. This results in the total water volume stored in the oceans of the world of about 1,350,000,000km³.
3. Water in the Lakes: The size of the lake and its depth coupled with the quantity of water supplied into it are important in determining the storage capacity. However, it is paramount in determining the storage capacity of any lake is the permeability of the country rock, the outflow and the evaporation rate. Small sized lakes usually have lower storage capacity while very extensive lakes have higher capacity and are relatively more permanent. Lakes may be either fresh or salt depending on whether they have outlet or not. The largest lake so far is the Caspian Sea with more than75% of the salt water volume in the world (about 80,00cm2km), this volume is about 3 times the volume of fresh water among all the five great lakes between United states and Canada. The total storage of salt water in lake with interior drainage is approximately 105,000 km³. Fresh water lakes provide a slightly greater amount of water storage than salt-water lakes, while none of the fresh water approaches the Caspian Sea in volume of storage.
4. Water in River Channel– While flow volume of many of the rivers of the world are fairly well known, it is more difficult to estimate the amount of water stored in the rivers at any time. The Amazon has a flow equals to about 20% of the total discharge of all the rivers in the world (more than 4 times the discharge of the Congo River) the river with the next greatest discharge are more than 10 times larger than the Mississippi River which ranks 7^th in the world. The total storage has been estimated to be about 0.7% of all the water stored in the lakes areas of the world (1700km3).
5. Water in Reservoirs: Reservoirs constitute a surface storage of water and it is necessary to make some estimate of this water volume. The total storage of water on the surface of the lake, river channels and reservoirs has been estimated to be 235,000km³.
6. Water Stored in Glacier and Icecaps: The amount of water held in frozen form in polar icecaps and mountains glacier varies somewhat throughout the year with freezing and melting. Estimates of the area of polar icecaps total about 6000000sqmiles (9654000km²) within all the combined artic and Antarctic circles more than 5million square miles of these icecaps are found in South Polar Region. The rest of the glacier ice occurs in the areas of other continental areas of the globe mostly at high elevation. It has been estimated that a total water volume of 25000000km³ of water is stored in the icecap and glacier of the world.
7. Water in the vegetation: Estimates of the total amount of water stored on the surface of the earth in the vegetation are extremely crude and of course, the amount varies appreciably from winter to summer or from season to season, since it is in such small amount. There is no reason to try to define any estimates. Thus, the total volume of water in the vegetation of the earth can be considered negligible in the overall water bodies.
8. Water in the Soils and Rocks-storage of water beneath the surface of the earth can be divided into three main categories:

• Water in the root zone of the soil which is about 3-4 ft (0.9144- 12192m).
• Water from the root zone to the 2500 ft depth (sea level) is (752m).
• Water from sea level to the average depth of the ocean is 9 12.500ft) which is about 3810m. Water below that depth is generally unavailable and is not considered. Comparatively, about a maximum value of about, 22000m³ of water is stored in the root zone, 4200000km² is found in the root zone to a depth of 2500ft and finally, 4600000m³ of water is found below 2500ft.

Uses of water

1. Transportation: Water in the rivers, lakes, and oceans are often used as a means of transport for conveying people and goods from one place to another for example Atlantic Ocean, river Niger and river Benue.
2. Hydroelectric Power: These various sources of water presents on the surface of the earth are demanded for the production of electricity for example the Kainji Dam, Akomsombo dam (river Volta in Ghana).
3. Mineral Deposit: Water bodies serve a source of mineral deposits for example, salt, Placer Gold, Tin, crude oil, Titanium, and Diamonds, Limestone and Gypsum are extracted from large water bodies. Read more on mineral resources.
4. Source of Food Man: Edible foods such as seaweeds and microalgae are widely eaten asseafoodby different humans around the world. However, shellfish like Squid, crab, octopus, oyster, shrimp, and lobster are harvested from saltwater environments.
5. Employment: The various water bodies such as lakes, rivers and oceans provide employment opportunities for people in various locations of the world. Ship builders, sailors, mariners, canoe carvers and fishermen are examples of such people.
6. Recreation and Tourism: Various water bodies also provide excellent facilities for swimming fishing and picnicking, boating skiing. Even activities such as golf, where there may not be any standing water, require plenty of water to make the grass on the course green. A larger water body like oceans provide beautiful scenery which attract tourists.
7. Domestic Use: Globally, household or personal water use is estimated to account for 15% of worldwide water use; since water is one of the most important necessities of life, it is highly needed in our homes for various uses. Domesticwateruse iswaterused for indoor and outdoor household purpose for instance for drinking, preparing food, bathing, washing of clothes and dishes, brushing of teeth, watering of yard and garden.
8. Industrial use: A large quantity of water is required by large industries like hydroelectric dams,thermoelectric power plants for cooling and generation of power. Large industries like oreandoilrefineries use water in chemical processes and manufacturing plants also use water as a solvent. Other example include various breweries, Iron smelting companies which use water for washing and processing of their raw materials.
9. Agricultural use: Some of the worlds farmers still farm without irrigation by choosing crops that match the amount of rain that falls in their area. However, some years are wet and others are extremely dry, in this case, farmer use water for irrigation to produce crops all year round.
10. Fishing: Fishing is a major activity which is common among the riverine people through which they earn their living. This activity is usually carried out all year round as to supply fish to various locations locally and internationally.
11. Environmental use: Environmental water may include water stored in impoundments and released for environmental purposes, but more often is water retained in waterways through regulatory limits of abstraction. Environmental water usage includes creating wildlife habitat, watering of natural or artificial wetlands, artificial lakes intended to create wildlife habitat for fish, water birds, and water releases from reservoirs timed to help fish spawn, or to restore more natural flow regimes.