Database results:
examBoard: Cambridge
examType: IGCSE
lessonTitle: Oceans as Drinking Water Sources
While oceans cover about 71% of Earth's surface and contain roughly 97% of all water on our planet, most of this water isn't immediately drinkable due to its high salt content. As freshwater sources become increasingly stressed by population growth, pollution and climate change, many regions are turning to the oceans as a potential solution to water scarcity.
Key Definitions:
Despite Earth being called the "Blue Planet," only about 2.5% of all water is freshwater and just 0.3% is easily accessible for human use. With over 2 billion people living in water-stressed countries and climate change intensifying droughts, finding new drinking water sources has become critical for human survival.
Oceans represent a virtually unlimited water supply, containing about 1.3 billion cubic kilometres of water. If we could efficiently convert seawater to freshwater, we could theoretically solve water scarcity issues worldwide. However, the challenge lies in making this conversion economically and environmentally sustainable.
There are several methods used to remove salt from seawater, each with its own advantages and limitations. The two main categories are thermal processes and membrane processes.
Thermal desalination involves heating seawater and collecting the freshwater vapour, leaving the salt behind. These methods have been used for centuries but have evolved significantly with modern technology.
Seawater is heated and passed through multiple chambers of progressively lower pressure, causing the water to "flash" into steam which is then condensed into freshwater. MSF plants are common in the Middle East where energy costs are lower.
Similar to MSF but uses the principle of reducing the ambient pressure in a series of vessels, allowing seawater to boil at lower temperatures. This method is more energy-efficient than MSF but still requires significant heat input.
Uses solar energy to evaporate water in a simple setup similar to a greenhouse. While low-tech and inexpensive, this method produces relatively small amounts of freshwater and requires large land areas.
Membrane processes use semi-permeable membranes to separate salt from water without requiring a phase change, making them generally more energy-efficient than thermal methods.
The most widely used desalination technology today. It works by applying pressure to push seawater through a semi-permeable membrane that allows water molecules to pass through but blocks salt and other impurities. RO plants can be built at various scales, from small portable units to massive facilities producing millions of litres daily.
Uses an electric field to move salt ions through ion-selective membranes, leaving freshwater behind. This method works best for brackish water (less salty than seawater) and is less energy-intensive for water with lower salt concentrations.
While desalination offers a solution to water scarcity, it comes with significant environmental considerations that must be addressed for sustainable implementation.
Desalination is energy-intensive, particularly thermal methods. Most plants run on fossil fuels, contributing to greenhouse gas emissions and climate change. Modern RO plants require about 3-4 kWh of energy per cubic metre of freshwater produced significantly more than conventional water treatment.
Intake systems can harm marine life through entrainment (trapping smaller organisms in water intake) and impingement (trapping larger organisms against screens). Brine discharge can create hypersaline zones near outfall pipes, affecting local marine ecosystems by changing water temperature, oxygen levels and salinity.
Several approaches can reduce the environmental footprint of desalination:
Singapore, a small island nation with limited natural freshwater, has developed one of the world's most comprehensive water management strategies. While not strictly ocean desalination, their NEWater programme recycles wastewater to drinking standards, meeting about 40% of Singapore's water needs. This is complemented by desalination plants that provide about 25% of the country's water supply. The country aims to meet 85% of its water needs through these alternative sources by 2060, reducing dependence on imported water from Malaysia. Singapore's approach demonstrates how integrated water management, including desalination, can create water security even in challenging geographic settings.
The cost of desalination has been a major barrier to widespread adoption, but technological improvements are gradually making it more competitive with conventional water sources.
The cost of desalinated water ranges from £0.50 to £2.50 per cubic metre, compared to £0.10 to £0.50 for conventional freshwater treatment. However, as freshwater becomes scarcer and desalination technology improves, this gap is narrowing.
Israel has become a world leader in desalination, with five major plants along its Mediterranean coast providing about 80% of the country's domestic water consumption. The Sorek desalination plant, one of the largest in the world, produces 624,000 cubic metres of water daily at a cost of about £0.40 per cubic metre one of the lowest costs globally for desalinated water. Israel's success comes from technological innovation, efficient plant design and a supportive regulatory environment. The country's experience shows how desalination can transform water security in arid regions when implemented with long-term planning and investment.
Researchers and engineers are developing new approaches to make desalination more efficient, affordable and environmentally friendly.
Uses the natural osmotic pressure difference between seawater and a "draw solution" to pull water through a membrane, requiring less energy than reverse osmosis. The challenge lies in efficiently separating the freshwater from the draw solution afterward.
Single-atom-thick carbon sheets with precisely controlled nanopores could allow water molecules to pass while blocking salt ions, potentially reducing energy requirements by 20-35% compared to conventional membranes.
Inspired by biological systems like mangrove trees and fish gills that naturally filter salt, these approaches aim to replicate nature's efficient desalination mechanisms in engineered systems.
Oceans represent a vast potential source of drinking water that could help address global water scarcity. While desalination currently faces challenges in terms of energy consumption, environmental impacts and costs, ongoing technological advances are making it increasingly viable. As part of an integrated approach to water management alongside conservation, recycling and protecting existing freshwater sources ocean desalination will likely play a growing role in ensuring water security in a changing climate.
For many coastal regions already experiencing water stress, the ocean isn't just a beautiful natural feature it's becoming an essential drinking water resource. The key challenge for the future will be harnessing this resource in ways that are economically accessible and environmentally sustainable.
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.