Water is one of the most important and valuable resources in the world, applying to industry, agriculture and transportation. More importantly, life on earth is impossible without water. There are currently over two billion people, or nearly 25 percent of the world’s population cannot obtain safe drinking water (Moe & Rheingans, 2006). Systems like these are attracting more attention as fresh water is becoming more scarce and expensive, which has been called attention to the severe problem of optimizing the use of fresh water resources. This purpose of this report is to investigate the feasibility of various techniques for providing fresh water in arid parts of the world. Firstly, the current situation of arid regions will be discussed. Then, it will look at the feasibility of different techniques to guarantee fresh water supply. Following this, it will explain the requirement of different options such as economic and technological. Finally, making some comparisons and giving recommendations.

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2.0 Background
It is known that 70 % of the earth’s surface is covered by water but 97% of this is saltwater and the other 3 % is fresh water that consists of surface and ground water. However, 2.5 % of fresh water are unusable while another 0.497 % is polluted water, only 0.003 % of the whole water on earth is available for drinking water. Figure (1) shows the availability of fresh water on earth.
Figure (1)
However, the 0.003 % of available water is extremely imbalanced distributed in the world, specifically in arid and semi-arid regions in North Africa and Middle East have a severe shortage of water so that in some regions the usable water is less than 1000 m³per capita and year. (see Figure. 2)
Fig.2: Water availability in the world measured in terms of 1000 m³ per capita/year [UNEP.org]
Arid areas of the world such as North Africa, South America, Australia and some areas of the America are faced with a problem of access to fresh water and could be enlarged (Clarke,1991). Arid regions are very dry and lacking vegetations because of their climate, temperature and rainfall. The climate in arid regions usually is a desert climate that its evaporation is larger than precipitation but with enough heat. Most arid regions only receive less than 250 mm (10 in ) of rainfall each year that may be difficult for arid regions to store fresh water.
3.0 Presentation of Options
Traditional methods of water supply are likely to be inadequate especially in arid regions with severe water scarcity. For satisfying fresh water demand in those areas, there are some feasible techniques such as water transfer project, desalination and application of isotope technique.
Water transfer is a project that moves water from one hydrologic basin to another, which is becoming viable in order to reduce the gap between supply and demand (Kazumba et al., 2011). In arid regions, the large water transfer project could be a solution to fulfil urban water demand because water availability is a different distribution (Mays, 2009). In Tanzania, the government is suggested to have large scale of the water transfer project to solve a shortage of water due to its difference of the seasonal precipitation change. (British Geological Survey, 2001)
Another technique is seawater desalination by removing salt and other minerals from saline water. Over the last several decades, a large number of seawater desalination technologies have been matured that can increase the supply of water in arid regions of the world (Khawaji et al., 2008). There are approximately 12000 desalination plants can supply dependable freshwater resources around the world, over 60% of which are located in the Middle East. (Cutright, 2007)
An alternative is applying isotope techniques in groundwater recharge. Isotope techniques are contributing to recognize the source of salinity and renewable groundwater (Fontes & Edmunds, 1989). Figure (3) shows changes in isotopic composition of water in different salinization processes (IAEA technical report series 210, 1981).
Figure (3)
In many areas, mainly in arid and semi-arid zones, the supply of fresh water is limited because of groundwater salinization (Gaye, 2001). The UNESCO (1987) claimed that isotopes are an accurate modern instrument for researching water resources. The problems of origin, distribution and attributes of water in a given region could be furnished solutions by using radioisotopes (Noone & Sturm, 2009)
4.0 Presentation of Requirements
To consider the three techniques mentioned above, they should satisfy variable requirements in order to guarantee their availability. In general, the economical and technical will be evaluated as factors affecting the three options mentioned above.
Economically, the water transfer project could be surprisingly expensive than others because it need to analyse its rationality (Dawoud & Abderrahman, 2006). For example, the high expenses of transport water large distances that may result in environmental side-effects such as ecological disruption and biodiversity decreased. In addition, the water transfer project has to value climate and geographic factors that possibly increase their project’s economic burden. Hence, economic support of such project can surpass their interests (Polyzou et al, 2010).
Technically, both seawater desalination and isotope technique need high technical requirement. Kalogirou (2005) argued that the process of desalination needs a larger amount of energy while Gaye (2001) considered isotope techniques have to follow regulations and keep records in any use of radioactive isotope. However, the three techniques are faced with how to protect the quality of water which is a significant problem for providing fresh water and hence they require a high level of technology. For instance, it is difficult to keep fresh water unpolluted when move water from long distances. And desalinated water can be harmful to human health because they use chemicals (Dawoud & Abderrahman, 2006).
5.0 Comparison of Options
5.1 Water transfer project
Planning water transfer projects likely to be the best option presented. Many researches indicate that water transfer can meet the huge water demand which will promote both industrial and agricultural developments (Lorang and Aggett, 2005). In arid regions, transfer water is a non-renewable resource that needs to be considered carefully, since these transfers satisfy presented demand but cannot last forever (Mays, 2009). Therefore, only in severely drought regions which have high economic capability such as America and Australia are suggested to build such projects.
5.2 Seawater desalination
Considering sea water accounts for 97% of the total quantity of water on earth, to fulfill both the qualitative and quantitative requirements for drinking water standards, the arid areas supposed to rely mainly on desalination especially in future decades because of recent cost-cutting innovations in the desalination process. Arid Australia willing to turn to desalination by considering the relatively low cost. The government is spending about 13.2 billion dollars on constructing desalination plants that will result in up to 30 percent of their water from the sea.(Onishi, 2010)
5.3 Application of isotope technique
Isotope technique is an advance tool that the application of isotope technique in hydrology makes isotopes as tracers in water resources development and management. (Gaye, 2001) The conventional methods often unable to provide deep research to these problems such as depleting groundwater quantity, deterioration in water quality and many other unpredictable natural events that affect the hydrological cycle, while isotope techniques provide a clear picture and helps in finding a suitable solution (Terwey, 1984). Therefore, isotope technique may be the effective method to provide fresh water in arid regions according to their extremely adverse conditions.
6.0 Conclusions & Recommendations
In conclusion, it appears that arid regions of the world can obtain water resource by applying different techniques such as interbasin water transfer, desalination, and the application of isotope techniques. In order to successfully provide fresh water to arid regions of the world, they are supposed to rely mainly on specific conditions of those areas that would be tackled effectively.
If an arid region is short of sufficient water resources but with the strong economic capability, it should own a large scale of the water transfer project as it may meet the huge industry and agriculture demand. However, arid regions that located close to a sea can consider investing in desalination as it costs relatively less and sustainable. But in the long run, application of isotope techniques will replace other water techniques due to its feasibility and availability considering the essential attribute of arid areas.