Water scarcity is now affecting 40 per cent of the world’s population and is set to worsen. In many countries there is insufficient water available from traditional sources, such as river flows and groundwater, to meet demands. Alternative, non-traditional water supplies are part of the solution to creating a water secure world.
Alternative water sources include desalination of sea water (or brackish water), and recycling or re-use of effluent from industrial and domestic wastewater treatment works. It is clear that desalination, together with water re-use technologies, will have increasing relevance to meeting potable water needs in the future, particularly in regions of the world subject to water scarcity.
Desalination has actually been practiced for over 50 years and is now a well established means of water supply in many countries. Two main processes have survived the evolution of desalination technology: thermal (evaporation) and membrane techniques. The cost of seawater desalination is nowadays down to 0.5-0.8 $/m3, and the decreasing cost tendency continues. Brackish water desalination is even cheaper; 0.2-0.35 $/m3. This means that, even though desalination is still more expensive than conventional water supply, its cost is low enough to be considered along with other options, such as water reuse.
In some situations where water is scarce, population growth has outstripped the availability of “conventional” freshwater sources or the cost of new water supplies rises, seawater desalination may be in fact the “least-cost” alternative for new supplies. The perception of desalination as a Cost-Prohibitive technology is true no more.
Only about 1% of drinking water is currently produced by desalination, supplied by more than 12,500 plants in more than 120 countries. Considering that almost one quarter of the world’s population lives less than 25 km from the coast, seawater could become one of the main sources of freshwater in the near future.
Recycling water is the process of removing solids and certain impurities from wastewater and using it again rather than discharging into surface water or the ocean. The reuse and recycling of water in industrial and domestic settings has the potential to reduce the consumption of water in these environments significantly. Harvested rainwater and recycled water can be used for activities such as toilet flushing, reducing overall domestic water consumption.
Currently in most locations, recycled water is used for non-potable purposes, such as irrigation, dust control, and fighting fires. There is controversy about possible health and environmental effects for even those uses, let alone for potable re-use. In some locations, however, (e.g. Singapore) waste water is given further treatment and is used indirectly by mixing with reservoir water and treating conventionally for drinking, a procedure known as Planned Indirect Potable Use.
Given the relatively small proportion of water that is used domestically the benefits of carrying out water recycling will be relatively small, though not insignificant and increasingly used in the water scarce Middle East. Industrial recycling of water has the potential for more significant savings of water. It also puts less pressure on natural water resources and can augment environmental flows. Harvesting rainwater via water butts has benefits not just in replacing mains water supplies in houses, but also in reducing quick runoff and thus the risk of flooding.