Water is a fundamental part of life, and for years everyone took it for granted. Recently, governments and concerned individuals worried that water resources were finite and could be lost to contamination or sudden loss, or from the pressure of large-farm irrigation that would create physical and chemical stresses.
Water Resources
Apart from its day-to-day use for drinking, irrigation, and marine life, water is used for many applications. It is used as a solvent (water dissolves more substances in greater quantities than any other liquid), for heating spaces (except for liquid ammonia, water has the highest heat transfer capacity, and is better suited for heating buildings), and for its ability to conduct electricity through dissociation, when acid is added (e.g., in automobile batteries). Therefore, it is necessary to understand the existence of water. For example, the presence of underground water depends not only on the creation of the storage facilities (between rocks, clays, and permeable soils) but also on nature’s ability to keep them supplied. We all know that there can be an abundance of water in one area or scarcity in other. To understand why water is present, we need to know the reasons for the uneven distribution of precipitation over the earth’s surface and the processes involved in the movement of water from place to place. In principle, the total volume of water on this planet is finite and constant, but the uneven distribution of water on the earth’s surface is due to hydrological cycle and weather patterns.
Water Resources
Apart from its day-to-day use for drinking, irrigation, and marine life, water is used for many applications. It is used as a solvent (water dissolves more substances in greater quantities than any other liquid), for heating spaces (except for liquid ammonia, water has the highest heat transfer capacity, and is better suited for heating buildings), and for its ability to conduct electricity through dissociation, when acid is added (e.g., in automobile batteries). Therefore, it is necessary to understand the existence of water. For example, the presence of underground water depends not only on the creation of the storage facilities (between rocks, clays, and permeable soils) but also on nature’s ability to keep them supplied. We all know that there can be an abundance of water in one area or scarcity in other. To understand why water is present, we need to know the reasons for the uneven distribution of precipitation over the earth’s surface and the processes involved in the movement of water from place to place. In principle, the total volume of water on this planet is finite and constant, but the uneven distribution of water on the earth’s surface is due to hydrological cycle and weather patterns.
In principle, it is solar energy that causes the uneven distribution of water on the earth’s surface.
The water itself serves as a thermal energy storage medium, which determines the three parameters of climate: air temperature, air pressure, and precipitation. When solar radiation strikes the earth’s surface, the earth is heated. At the Equator, there is a net heat gain, while at the poles; there is a net heat loss. Through the movement of the oceans and the atmosphere, the surplus heat moves toward the poles. The cool air is heated when it reaches the earth’s surface and rises back into the atmosphere, while the warm rising air that contains water through evaporation eventually cools and falls back to earth as rain. Water from the sea evaporates to form clouds, returns to the earth as precipitation, and via streams, rivers, and infiltration, returns to the sea. This process is called the hydrologic cycle. This cycle creates certain weather patterns so that one location is dry while another location is wet. Therefore, the sources of water vary from one locality to another. However, the availability of groundwater depends not only on the hydrologic cycle and weather pattern. It also depends upon the formation of aquifer systems. The formation of aquifers can be from weathering, erosion, glacial deposits, sedimentary rocks, alluvial aquifers, and/or igneous and metamorphic rock aquifers. There are two main water sources: surface water and groundwater. Surface water sources are rivers, streams, man-made ponds or reservoirs, lakes, and seas. Streams are generally seasonal; depending on the size and tributaries, river-water sources can be seasonal or year round. Seasonal water sources require man-made dams or reservoirs for water supply and irrigation purposes. However, water resources from year-round rivers or lakes do not require such storage.
Generally, surface waters require treatment for domestic water supply, and this will be discussed in the following chapters.
Groundwater resources are formed when the surface is over-saturated and the excess water filters down. The depth of the soil water zone varies from about 1 meter (m) to 9 m (3 feet (ft) to 30 ft).
Water is also lost by transpiration and evaporation. Soil undergoes wide variations in moisture content—from complete saturation to a total lack of moisture. Water is held in the soil by molecular or capillary attraction, acting against the force of gravity. Molecular attraction holds water in a thin film on the surface of each soil particle. Capillary attraction holds water in the smallest spaces between soil particles. Water begins to percolate downward under the force of gravity when the water-holding capacity of the capillary forces is exceeded. The region immediately below the soil water zone is called the intermediate zone. Most water in this zone will move downward, has no in-situ use, and cannot be recovered. There is a capillary fringe at the bottom of the intermediate zone where groundwater is drawn upward by capillary forces. Depending on the kind of aquifer, water may migrate upward more than 3 m (Driscoll 1986).
Well-sorted, fine sediments are most effective at holding water and are often completely saturated within the capillary fringe zone; coarse sediments are not as effective in holding water. The groundwater table lies at the very bottom of the capillary zone. Generally, subsurface water used for domestic purposes and irrigation is pumped from below the groundwater table. However, groundwater can also be springs or artesian wells, where water is forced from the aquifer by compaction caused by the weight of overlying sediments or a well that derives its water from a confined aquifer in which the water level is above the ground surface. In such cases, groundwater is capped at the surface (at the eye of the spring or artesian well).
Groundwater found in shallow wells can generally be extracted using hand pumps or with a simple pulley and bucket. Such wells can be dug by hand or bored using earth augers. There are three main types of earth augers: large-diameter bucket augers, solid-stem augers, and hollow stem augers. Large-diameter bucket augers are most commonly used to drill up to about 45 m (150-ft) deep and up to 1.2 m (48–inch [in]) diameter wells. Solid-stem augers can drill up to 35 m (120 ft) deep and up to 600 millimeters (mm) (24 in) in diameter. The most common depth for hollow-stem augers in stable formations are 35 m (120 ft) for a 150 mm (6 in) diameter hollow stem auger and about 12 m deep for a 300 mm (12-in) diameter hollow-stem auger (Driscoll 1986). Generally, deep wells are drilled using drilling machines. There are several types of drilling methods, depending on the geologic formation and the depth and diameter of the well.
Particular drilling methods become dominant in certain areas because they are most effective in penetrating the local aquifers and thus offer cost advantages. Some of the most common drilling machines are cable tool drills, direct- and reverse-circulation rotary drills, and air drills. Rotary drilling machines are mostly used to reach greater depths and to increase drilling speeds.
Normally drilling fluids (air, clean water, and mixtures of special-purpose materials) are essential for efficient rotary drilling. However, direct rotary drilling is very expensive because drill bits are costly and drilling rigs require a high level of maintenance. Reverse circulation drilling is generally most successful in soft sedimentary rocks and unconsolidated sand and gravel where the static water level is 3 m (10 ft) or more below ground level. This drilling method is the least expensive for drilling large-diameter holes in unconsolidated formations.
Springs are commonly found at the foot of mountains. Mountains are also sources of streams, and many streams flow into rivers. When streams and rivers flow over a flat area, the surrounding area will generally have good underground water because water soaks into the aquifer. Such areas are generally good for shallow wells. Although surface and rainwater infiltration are the main sources for enriching underground water sources, water also flows underground through fractured rocks and aquifers, depending on the hydrological formations of the ground. The best aquifers are coarse sand and gravel, limestone openings, sandstone, or fractured rocks, and aquifers, such as clay, silt, and solid metamorphic rock like marble have very minimal water penetration. An aquifer on the surface of the ground, having a reasonable depth and followed by a layer of impermeable materials (e.g., solid rock, silt, or clay), is considered to be a good catchments area for underground water. Therefore, a detailed geological survey should be made before drilling. More than 40% of the wells drilled in developing countries for domestic water supply are abandoned due to lack of sufficient water.
Raw Water Quality
The source of the water determines its characteristics. Generally, surface water is exposed to contamination due to human, animal, and industrial activities upstream. Surface water can be contaminated with both pathogenic and non-pathogenic organisms and suspended solid particles from precipitation or runoffs. On the other hand, groundwater is usually clear and odorless. Groundwater does not usually contain suspended solid particles or bacteria or organic matter, but does usually contain dissolved mineral ions (minerals are generally dissolved in water and the term total dissolved solids (TDS) refers to them). The type and concentration of these dissolved minerals can affect how the groundwater can be used. If certain minerals are present in excessive amounts, certain types of treatment may be necessary to change or remove the dissolved mineral before using the groundwater for its intended purpose. However, studies show that moderate TDS levels have some health benefits. Although groundwater may not have bacteria, there is a risk of contamination, especially for shallow wells, from human and animal activities in the area. Contaminants can seep into the ground from the top of the borehole. Therefore, the area surrounding the borehole should have proper drainage to keep it dry, and the borehole should be properly capped.
The water quality level varies, depending on the intended purposes. Water used for irrigation can be very low quality, as long as it is not salty, which might burn the soil and crops. On the other hand, drinking water should fulfill the water quality standard guidelines set by national governments and the World Health Organization (WHO). Sources of contaminants are characterized as physical, chemical, bacteriological, and radiological. The WHO has guidelines for five categories of contaminants for drinking water:
1. Microbiological and biological standards (microorganisms and other organisms)
2. Inorganic constituents that pose health risks (arsenic, cadmium, nitrate, lead, and sodium)
3. Organic constituents (benzene, phenols, dichlorodiphenyltrichloroethane (DDT), and others)
4. Aesthetic guidelines (odor, taste, hardness, and color)
5. Radioactivity guidelines (mostly for groundwater).
The water itself serves as a thermal energy storage medium, which determines the three parameters of climate: air temperature, air pressure, and precipitation. When solar radiation strikes the earth’s surface, the earth is heated. At the Equator, there is a net heat gain, while at the poles; there is a net heat loss. Through the movement of the oceans and the atmosphere, the surplus heat moves toward the poles. The cool air is heated when it reaches the earth’s surface and rises back into the atmosphere, while the warm rising air that contains water through evaporation eventually cools and falls back to earth as rain. Water from the sea evaporates to form clouds, returns to the earth as precipitation, and via streams, rivers, and infiltration, returns to the sea. This process is called the hydrologic cycle. This cycle creates certain weather patterns so that one location is dry while another location is wet. Therefore, the sources of water vary from one locality to another. However, the availability of groundwater depends not only on the hydrologic cycle and weather pattern. It also depends upon the formation of aquifer systems. The formation of aquifers can be from weathering, erosion, glacial deposits, sedimentary rocks, alluvial aquifers, and/or igneous and metamorphic rock aquifers. There are two main water sources: surface water and groundwater. Surface water sources are rivers, streams, man-made ponds or reservoirs, lakes, and seas. Streams are generally seasonal; depending on the size and tributaries, river-water sources can be seasonal or year round. Seasonal water sources require man-made dams or reservoirs for water supply and irrigation purposes. However, water resources from year-round rivers or lakes do not require such storage.
Generally, surface waters require treatment for domestic water supply, and this will be discussed in the following chapters.
Groundwater resources are formed when the surface is over-saturated and the excess water filters down. The depth of the soil water zone varies from about 1 meter (m) to 9 m (3 feet (ft) to 30 ft).
Water is also lost by transpiration and evaporation. Soil undergoes wide variations in moisture content—from complete saturation to a total lack of moisture. Water is held in the soil by molecular or capillary attraction, acting against the force of gravity. Molecular attraction holds water in a thin film on the surface of each soil particle. Capillary attraction holds water in the smallest spaces between soil particles. Water begins to percolate downward under the force of gravity when the water-holding capacity of the capillary forces is exceeded. The region immediately below the soil water zone is called the intermediate zone. Most water in this zone will move downward, has no in-situ use, and cannot be recovered. There is a capillary fringe at the bottom of the intermediate zone where groundwater is drawn upward by capillary forces. Depending on the kind of aquifer, water may migrate upward more than 3 m (Driscoll 1986).
Well-sorted, fine sediments are most effective at holding water and are often completely saturated within the capillary fringe zone; coarse sediments are not as effective in holding water. The groundwater table lies at the very bottom of the capillary zone. Generally, subsurface water used for domestic purposes and irrigation is pumped from below the groundwater table. However, groundwater can also be springs or artesian wells, where water is forced from the aquifer by compaction caused by the weight of overlying sediments or a well that derives its water from a confined aquifer in which the water level is above the ground surface. In such cases, groundwater is capped at the surface (at the eye of the spring or artesian well).
Groundwater found in shallow wells can generally be extracted using hand pumps or with a simple pulley and bucket. Such wells can be dug by hand or bored using earth augers. There are three main types of earth augers: large-diameter bucket augers, solid-stem augers, and hollow stem augers. Large-diameter bucket augers are most commonly used to drill up to about 45 m (150-ft) deep and up to 1.2 m (48–inch [in]) diameter wells. Solid-stem augers can drill up to 35 m (120 ft) deep and up to 600 millimeters (mm) (24 in) in diameter. The most common depth for hollow-stem augers in stable formations are 35 m (120 ft) for a 150 mm (6 in) diameter hollow stem auger and about 12 m deep for a 300 mm (12-in) diameter hollow-stem auger (Driscoll 1986). Generally, deep wells are drilled using drilling machines. There are several types of drilling methods, depending on the geologic formation and the depth and diameter of the well.
Particular drilling methods become dominant in certain areas because they are most effective in penetrating the local aquifers and thus offer cost advantages. Some of the most common drilling machines are cable tool drills, direct- and reverse-circulation rotary drills, and air drills. Rotary drilling machines are mostly used to reach greater depths and to increase drilling speeds.
Normally drilling fluids (air, clean water, and mixtures of special-purpose materials) are essential for efficient rotary drilling. However, direct rotary drilling is very expensive because drill bits are costly and drilling rigs require a high level of maintenance. Reverse circulation drilling is generally most successful in soft sedimentary rocks and unconsolidated sand and gravel where the static water level is 3 m (10 ft) or more below ground level. This drilling method is the least expensive for drilling large-diameter holes in unconsolidated formations.
Springs are commonly found at the foot of mountains. Mountains are also sources of streams, and many streams flow into rivers. When streams and rivers flow over a flat area, the surrounding area will generally have good underground water because water soaks into the aquifer. Such areas are generally good for shallow wells. Although surface and rainwater infiltration are the main sources for enriching underground water sources, water also flows underground through fractured rocks and aquifers, depending on the hydrological formations of the ground. The best aquifers are coarse sand and gravel, limestone openings, sandstone, or fractured rocks, and aquifers, such as clay, silt, and solid metamorphic rock like marble have very minimal water penetration. An aquifer on the surface of the ground, having a reasonable depth and followed by a layer of impermeable materials (e.g., solid rock, silt, or clay), is considered to be a good catchments area for underground water. Therefore, a detailed geological survey should be made before drilling. More than 40% of the wells drilled in developing countries for domestic water supply are abandoned due to lack of sufficient water.
Raw Water Quality
The source of the water determines its characteristics. Generally, surface water is exposed to contamination due to human, animal, and industrial activities upstream. Surface water can be contaminated with both pathogenic and non-pathogenic organisms and suspended solid particles from precipitation or runoffs. On the other hand, groundwater is usually clear and odorless. Groundwater does not usually contain suspended solid particles or bacteria or organic matter, but does usually contain dissolved mineral ions (minerals are generally dissolved in water and the term total dissolved solids (TDS) refers to them). The type and concentration of these dissolved minerals can affect how the groundwater can be used. If certain minerals are present in excessive amounts, certain types of treatment may be necessary to change or remove the dissolved mineral before using the groundwater for its intended purpose. However, studies show that moderate TDS levels have some health benefits. Although groundwater may not have bacteria, there is a risk of contamination, especially for shallow wells, from human and animal activities in the area. Contaminants can seep into the ground from the top of the borehole. Therefore, the area surrounding the borehole should have proper drainage to keep it dry, and the borehole should be properly capped.
The water quality level varies, depending on the intended purposes. Water used for irrigation can be very low quality, as long as it is not salty, which might burn the soil and crops. On the other hand, drinking water should fulfill the water quality standard guidelines set by national governments and the World Health Organization (WHO). Sources of contaminants are characterized as physical, chemical, bacteriological, and radiological. The WHO has guidelines for five categories of contaminants for drinking water:
1. Microbiological and biological standards (microorganisms and other organisms)
2. Inorganic constituents that pose health risks (arsenic, cadmium, nitrate, lead, and sodium)
3. Organic constituents (benzene, phenols, dichlorodiphenyltrichloroethane (DDT), and others)
4. Aesthetic guidelines (odor, taste, hardness, and color)
5. Radioactivity guidelines (mostly for groundwater).
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