The use of water has increased manifold as economic growth in many developing countries has picked up and additional land is being brought under cultivation to meet the growing food demand . Many countries such as parts of Australia, southwest part of America, India and western Europe are receiving about 10 per cent less rainfall than before, due to changing rainfall patterns resulting from climate change and global warming. According to reports, annual inflows into water reservoirs had fallen to 150 billion litres a year by late 1990’s from 300 billion litres in the 1980’s.
Pakistan may also face serious water shortage in the coming years, as glaciers — one of its main water sources — are melting at a fast speed. Climate change and global warming are also adversely affecting the rainfall pattern and water availability..
In order to improve water supply, various measures are taken, such as construction of small and mega dams and building of reservoirs to store rain water, using of ground-water by installing tube-wells and water recycling etc. Desalination of sea-water has been added recently to the list.
For a long time, desalination of sea-water remained a subject-matter of serious criticism. It was opposed mainly on two grounds. First, because it consumed lot of energy – often generated by coal – which made it unfriendly to environment. Secondly, because desalination was too expensive. Even the cheapest desalinated water could cost eight times more than the traditional ground- water sources, which might be tapped for as little as five cents per cubic metre.
However, due to the looming global water shortages and the concerns of various nations about water security, sea-water desalination was gradually accepted as a possible option to fight water scarcity.
The US press reports that as many as 75 major desalination projects are in various stages of development world-wide. The US has one such plant north of San Diego and some more plants are likely to come up soon in various other states. Several Australian cities are setting up desalination plants. The largest, near Melbourne, may cost as much as $2.5 billion. Similar facilities are planned in Spain and India, while London is reported to be planning a $400 million plant along the river Thames.
One of the desalination plants in Australia, opened in 2006, is being treated as a model for the developed world. The $360 million plant at Perth draws nearly 50,000 gallons of water from the Indian Ocean every minute. The water is then run through special filters that separate salt from water, producing about 25,000 gallons of drinkable water.
Latest desalination facilities use a process known as reverse osmosis in which water is pushed under high pressure through porous membranes that separate the salt. The process needs energy, in order to raise the pressure and force the water through membranes.
Engineers have been able to improve membranes so that they can now separate salt from water more effectively. The system includes a pre-treatment device to remove large particles from water before it goes through the process. Besides, the modern facility includes an energy recovery device that makes it possible to recycle as much as 90 per cent of the energy consumed in the process.
The desalination plant at Perth was in running condition by late 2006. The plant includes a first-stage facility to remove silt and other impurities from the water, piped in from the adjacent sea. Water is then moved into a large building where it is pressurised and pushed through membranes in high-tech vessels. It is then treated with chlorine and piped into a reservoir, from which it is supplied to the local population. The left-over salt is flushed back into the ocean.
The plant is regarded as a model, because it had tried to address both the environmental and financial concerns with regard to such plants. In the first instance, it uses energy generated from wind, which is environment-friendly and, secondly, the system used in the plant had been upgraded to reduce its cost. Officials consider the project so successful that they are planning to build a second $875 million desalination plant which would enable the local population to meet one-third of its total water requirement from the ocean, thus reducing its dependence on rain-fed reserves.
Pakistan has been experiencing water shortage for the last many years, as a result of which not only is the performance of its agriculture sector adversely affected but the population – particularly in the urban areas – is also put to lot of inconvenience, at times.
The government should lose no time in starting the construction of small as well as mega dams. Particularly, the mega dams would help in low-cost and environment-friendly power generation, besides bringing about significant improvement in the water supply situation. Sea-water desalination, which consumes lot of energy, cannot be an option in the short run, as the country is already faced with power shortage. However, in the long run, we may have to resort to this option when other water sources start drying up.
To prepare the country for such an eventuality, power generation may be boosted by utilising the 185 billion tons coal reserves and constructing mega dams, as soon as possible. Besides, wind farms may be set up for power generation from wind in the coastal areas of Sindh and Balochistan, which may be possible sites for the desalination plants, in future.