ABSTRACT: Water pollution is one of the main concerns of the world today. Much other pollution threatens water supplies, but the most wide spread, especially in under developed countries, is the discharge of raw sewage into natural waters. It is estimated that around 80% of water consumed by a household is let to the drains of sewage as waste water. In addition to sewage, non-point source pollution such as agriculture run-offs is a significant source of pollution in some part of the world, along with urban storm water run-offs and chemical water dumped by industries and government. Many areas of ground water and surface water are now contaminated with heavy metals, persistent organic pollutants (POPS) and nutrients that have an adverse effect on health. Exposure to polluted water can cause diarrhea, skin irritation, respiratory problems and other diseases, depending on the pollutant that is in the water body. Among these, malaria is undoubtedly the most widely distributed and causes most damage to human health. Thus, water can be considered as a resource and a problem, because the problems associated with water pollution have the capabilities to disrupt life on our planet to a great extent. Congress has passed laws to combat water pollution, thus, acknowledging the fact that water pollution is indeed a serious issue.
Water is one of the critical inputs for the sustenance of mankind. It is used by both terrestrial and aquatic environment for various activities, balancing the ecological system and global environment. Water is the important natural resources which are abundant in nature and covers about 71 percent of the earth surface (Wolf, 2001). However, only 1% of the water resource is available as fresh water (i.e. surface water, river, lakes, stream and underground water) for human consumption and other activities. The major uses of water are for irrigation (30%), thermal power plant (50%), while other uses are domestic (7%) and industrial consumption (12%) (Farid, 2003).
Against the natural average target of 135 pcd of water and 180 pcd per capital in large cities, the per capital available is low and ranges from 165 lpcd in a few larger town to about 50 lpcd in most smaller towns. The availability of water in Urban slums is about 27 lpcd. Urbanization has given rise to a number of environmental problems such as water supply, waste water generation and its collection, treatment and disposal in Urban areas. In most cases, waste water is let out untreated and its either percolate into ground and in turn contaminate the ground water or is discharged into the natural drainage system causing pollution in downstream areas.
Due to negligence, ground water is also increasingly getting contaminated. Most of the existing collecting systems discharge directly to the receiving water without treatment. Gerbage, domestic waste otherwise, is directly dumped into its water bodies or road side, which has often been washed into streams and lakes.
The municipalities disposes off their treated or partly treated and untreated waste water into natural drains joining rivers or lakes or used on land for irrigation or fodder cultivation or into sea or combination of these. Toxics chemical from sewage water transfer to plant and enter the food chain and affect public health. Pathogens occurring in the sewage water directly affect the mammals causing severe diseases. It is estimated that around 80% of water consumed by a household is let to the drains of sewage as waste water. Thus waste water can be considered as both a resource and a problem. Waste water and its nutrient content can be used extensively for irrigation and other ecosystem services. Its reuse can deliver positive benefits to the farming community, society and municipalities. However, waste water reuse also exerts negative effects on humans and ecological systems which need to be identified and assessed.
Before one can endorse waste water irrigation as a means of increasing water supply for agriculture, a thorough analysis must be undertaken from an economic perspective as well. In this regard, the comprehensive costs and benefits of such waste water reuse should also be evaluated. Moreover, the economic effects of waste water irrigation need to be evaluated not only from the social, economic and ecological stand point, but also from the sustainable development perspective.
1.1 SOURCES OF FRESH WATER
1.1.1 Surface Water
Surface water is water in a river, lake or fresh water wetland. Surface water is naturally replenished by precipitation and naturally cost through discharge to the oceans, evaporation and sub-surface seepage. Although the only natural input to any surface water system is precipitation within its water shed, the total quantity of water in that system at any given time is also dependent on many other factors. These factors include storage capacity, wetlands and artificial reservoirs, the permeability of the soil beneath these storage bodies, the run-off 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 lost.
Human activities can have a large impact on these factors. Humans often increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans often increase run-off quantities and velocities by paving areas and channelizing stream flow (Winpenny, 1991).
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, many farms require large quantities of water in the spring and no water at all in the winter. To supply such a farm with water, a surface water, system may require a large storage capacity to collect water throughout the year and release it in a short period of time. Other users have a continuous need of water for cooling. To supply such a power plant with water, a surface water system only needs enough storage capacity to fill in when average stream flow in below the power plant’s need (Wolf, 2000). Nevertheless, over the long-term, the average rate of precipitation within a water shed is the upper bound for average consumption of natural surface water from that watershed.
Natural surface water can be augmented by importing surface water from another watershed through a canal or pipeline. It can also be artificially augmented from any of the other sources listed here. However, in practice the quantities are negligible. Humans can also cause surface water to be ‘lost’ (i.e become unusable through pollution (Homer-Dixon, 1999).
1.1.2 Sub-surface Water
Sub-surface water or ground water is fresh water located in the pore space of soil and rocks. It is also water that is flowing within aquifers below the water table sometimes it is useful to make a distinction between sub-surface water that is closely associated with surface water and deep sub-surface water in an aquifer (sometimes called ‘fossil’ water).
Sub-surface water can be thought in the same terms as surface water: inputs, outputs and storage the critical difference is due to its slow rate of turnover. Sub-surface water storage is generally much larger compared to inputs than it is for surface water. This difference makes it easy for humans to use sub-surface water unsustainably for a long time without severe consequence.
Nevertheless, over the long-time, the average rate of seepage above a sub-surface water source is the upper bound for average consumption of water from that source. The natural input to sub-surface water is seepage from surface water. The natural outputs from sub-surface water are springs and seepage to the oceans.
If the surface water source is also subject to substantial evaporation, a sub-surface water source may become aligned. This situation can occur naturally under endothermic bodies of water, or artificially under irrigated farmland. In coastal areas, human use of a sub-surface water source may cause the direction of seepage to ocean to reverse which can also soil salinization. Human can increase the input to a sub-surface water source by building reservoirs or detention ponds. Water in the ground are in sections called aquifers. Rain rolls down and comes into these. Normally, an aquifer is near to the equilibrium in its water content. The water content of an aquifer normally depends on the grain sizes. This means that, the rate of extraction may be limited by poor permeability.
Desalination is an artificial process by which saline water (generally sea water) is converted to fresh water. The most common desalination processes are distillation and reverse osmosis. Desalination is currently expensive compared to most alternation sources of water and only a very small fraction of total human use is satisfied by desalination. It is only economically practical for high valued uses (such as household and industrial users) in arid areas. The most extensive use is in the Persian Gulf (Adeel, 2001).
1.1.4 Frozen Water
Several schemes have been proposed to make use of icebergs as a water source. However, to date, this has only been done for novelty purposes. Glacier run-off is considered to be surface water.
1.2 USES OF FRESH WATER
It is estimated that 69% of worldwide water use is for irrigation, with 15-35% of irrigation withdrawals being unsustainable. In some areas of the world, irrigation is necessary to grow any crop at all. In other areas, it permits more profitable crops to be grown or enhances crop yield. Various irrigation methods involve different trade-offs between crop yield, water consumption and capital cost of equipment and structure. Irrigation method such as most furrow and overhead sprinkled irrigation are usually less expensive but also less efficient because much of the water evaporates or runs-off. More efficient irrigation, surge irrigation and some types of sprinkler systems where the sprinklers are operated near ground level. These types of systems, while more expensive can minimize run-off and evaporation (Farid et al, 2003).
It is estimated that 15% of world wide water use is industrial. Major industrial users include power plants, which use water for cooling or as a power source (i.e. hydroelectric plants) ore and oil refineries, which use water in chemical processes, and manufacturing plants, which use water as a solvent (Ravallhin, 2001). The portion of industrial water usage that is consumptive varies widely, but as a whole is lower than agricultural use.
It is estimated that 15% of worldwide water use is for household purposes. These include drinking water, bathing, cooking, sanitation and gardening. Basic household water requirements have been estimated at around 50 litres per person per day, excluding water for gardens.
Recreational water use is usually a very small but growing percentage of total water use. Recreational water use is mostly tied to reservoirs. If a reservoir is kept fuller than it would otherwise be for recreation, then the water retained could be categorized as recreational usage. Release of water from a few reservoirs is also timed to enhance whitewater boating, which also could be considered a recreational usage. Other examples are anglers, water skier’s, nature enthusiasts and swimmers.
Recreational usage is usually non-consumptive. Golf courses are often targeted as using excessive amount of water especially in drier regions. It is however unclear whether recreational irrigation (which would include private gardens) has a noticeable effect on water resource. This is largely due to the unavailability of reliable data. Some government including the California government have tabeled golf course usage as agricultural in order to deflect environmentalists charges of wasting water. However, using the above figures as a basis, the actual statistical effect of this reassignment is close to zero (Roster et al, 2006).
Explicit environmental water use is also a very small but growing percentage of total water use. Environmental water usage includes artificial wetlands, artificial lakes intended to create wildlife’s habitats, fish ladders around dams and water release from reservoirs timed to help fish spawn (Goel and Sharmay, 1996).