Experts explore unconventional water sources

A new book, Unconventional water resourcessays unconventional water supplies can help many of the 1 in 4 people on Earth who face water shortages for drinking, sanitation, agriculture and economic development.

Based on up-to-date information and data, and with contributions from scientists, experts and practitioners around the world, the book presents the potential of different types of unconventional water resources – tapping deep offshore groundwater and on land, for example, reusing water, physically moving water to areas where water is scarce, and more.

The book was published by Springer and compiled by experts from the United Nations University Institute for Water, Environment and Health (UNU-INWEH), the UNU Institute for the Integrated Management of Material Flows and Resources (UNU-FLORES) and the UNU Food and Agriculture Organization (FAO).

“As climate change worsens and population increases around the world, water shortages pose a major threat to human development and security, making this authoritative analysis on unconventional water resources in both timely and important,” UNU-INWEH Director Vladimir Smakhtin said in a press release.

“Harnessing the potential of unconventional water sources could benefit billions of people,” said Manzoor Qadir, the book’s lead editor. “These springs will be key to building a future in the drylands.”

The book identifies six broad categories of unconventional water sources:

1) Harvest water from the air

The atmosphere contains about 13,000 km3 of water vapour, some of which can be captured by cloud seeding and water collection from fog and mist.

Cloud seeding or rain enhancement

Cloud seeding can increase rainfall by up to 15% under the right conditions, and studies show that rain enhancement can work with reasonable cost-benefit ratios. A growing number of countries plan to improve rainfall in response to water shortages and other societal needs.

Fog Harvest

Remote communities in Chile, Morocco and South Africa have used vertical mesh nets to harvest fog for over 100 years, and there are viable sites for fog harvesting on every continent. Advances in technology have made it possible to develop highly productive, relatively inexpensive and environmentally friendly designs for collecting potable water – more than 20 liters per day of dense fog for every square meter of mesh. The mesh, at an overall cost of less than $250 per square meter and used at a site that experiences fog for half the year, can produce over a decade approximately 35,000 liters per square meter at an average cost per liter of less than 1/10th. of a penny.

2) Desalination

Every day, desalination contributes more than 100 million cubic meters of water, supporting around 5% of the world’s population. This volume is expected to double by 2030 while costs will fall by 50%. New developments in desalination will likely make it the cheapest unconventional water supply resource in the world, especially in low-income countries where desalinated water production remains far from reality.

While desalination is energy intensive today, innovative technologies such as nanoparticle reinforced membranes and forward osmosis reduce energy inputs by 20-35%. Meanwhile, desalination produces huge amounts of brine, a pollutant of growing concern where it is discharged. New technologies capable of extracting salts, magnesium and other metals from brine into commercially viable products could offset the cost of desalinated water production over the next decade.

3) Water reuse

Municipal wastewater

Advanced municipal wastewater treatment systems provide a source of water while protecting high-quality fresh surface and groundwater.

Today, around 70% of municipal wastewater in high-income countries is treated, but this figure drops to just 8% in low-income countries. The annual volume of untreated municipal wastewater is estimated at 171 km3. Much of it is dumped into the environment, reducing water quality in many parts of the world.

Treated wastewater is increasingly used to recharge underground aquifers that provide drinking water in a number of countries. Treated wastewater provides 25% of Windhoek, Namibia’s drinking water supply and meets 40% of Singapore’s demand.

San Diego, California, and other US cities also get some of their drinking water this way, while Israel and other places use treated sewage to meet nearly a quarter of its water needs. agricultural water. The acceptance of reused wastewater by populations and decision-makers remains a challenge.

Agricultural drainage water

Only 1/5th of all cultivated land is irrigated but it produces 40% of the world’s food. Compared to rainfed agriculture, irrigated agriculture is, on average, at least twice as productive per unit of land because it allows the intensification of production and the diversification of crops. And even more food can be grown using the same amount of water through better conservation and reuse of irrigated agricultural drainage water. The latter requires additional care and management because drainage water will always be more saline than the irrigation water from which it is generated.

Salt-tolerant crops are increasingly making it possible to grow crops in salt water. Cycling and mixing are key management options where one field uses irrigated drainage water from another and then a third uses that drainage water mixed with fresh water. Water and salt from super saline drainage can be harvested by solar evaporation.

4) Exploit groundwater

The volume of renewable groundwater can reach 500,000 km3, although much of it tends to be brackish. The seabed near the coasts contains considerable volumes of fresh to brackish water.


There are large quantities (estimated between 300,000 and 500,000 km3) of water in shallow aquifers on continental shelves around the world. These aquifers lie less than 100 km offshore, created millions of years ago when sea levels were much lower.

About 3,000 years ago, the ancient Syrians placed an inverted funnel over an offshore spring to deliver about 1,500 liters per second to the city of Tyre. In the 1970s, exploratory drilling off the east coast of the United States found little oil or gas, but identified large amounts of fresh to brackish water.

Today, new methods of marine electromagnetic exploration are providing detailed images of offshore fresh waters. These images, combined with horizontal drilling technologies, can make available the production of economically significant volumes of fresh water to be pumped to shore for at least 30 years. To date, no freshwater resources at sea have been exploited.

Coastal brackish groundwater

Deep inland aquifers containing brackish or saline water in volumes estimated at millions of cubic kilometers. As shallow freshwater sources have declined, there has been an exponential growth in reverse osmosis brackish water desalination plants for drinking water across the United States. In Israel and Spain, desalinated water produced from brackish water is also used for the production of high-value crops.

Reducing the high costs involved can be accomplished by using electromagnetic surveys to find relatively abundant fresh/brackish water sources and siting desalination plants there. Improving the efficiency of these facilities will enable wider use of desalinated water in agriculture. Notably, deep underground aquifers can hold hot brackish water that can first be used for geothermal heating in greenhouses and aquaculture facilities and then desalinated, reducing overall costs.

5) Small-scale rainwater harvesting

In dry environments, more than 90% of rainwater is typically lost through evaporation and surface runoff. Rainwater harvesting through micro-catchment offers a unique opportunity to capture water for agricultural production and local needs. It is an ancient practice that uses a wide range of techniques from rooftop and cistern collection to agricultural and landscape systems, including contour ridges, bunds, small runoff ponds and strips. .

Even in very dry areas, collecting rainwater from three quarters of the land and using it on the remaining quarter can often provide plenty of water for livestock watering and shrub production.

6) Move water physically

ballast water

Ships carry around 90% of the world’s traded goods and discharge some 10 billion tonnes of ballast water (10 km3) every year. Under the International Convention for the Control and Management of Ships’ Ballast Water and Sediments, all ships of 400 gross tonnage or more must have onboard treatment options to desalinate ship water. ballast, remove invasive aquatic organisms and harmful chemical compounds, and are usable for other economic purposes. activities such as irrigation. This water could be sold to port cities in arid regions.

A study has estimated that tankers and liquefied natural gas (LNG) ships docking in the port city of Abu Dhabi in the United Arab Emirates could transfer their ballast water to an onshore water treatment plant. Ports with onshore desalination facilities could also sell treated ballast water.


The more than 100,000 Arctic and Antarctic icebergs that melt each year in the ocean contain more fresh water than the world consumes. Harvesting icebergs for fresh water has long been discussed but is not considered practical.

However, icebergs are towed to provide water for 700 residents of Qaanaaq, Greenland. Iceberg towing is done in Newfoundland and Labrador to prevent collisions with offshore oil and gas platforms as well as for fresh water and other uses.

Towing icebergs over long distances has never been attempted due to the large loss of water volume and potential ice breakage during towing. However, an analysis of the financial feasibility of towing icebergs to Cape Town, South Africa, suggests that it is an economically attractive option if the icebergs to be towed are large enough (i.e. say 125 million tons). Wrapping icebergs in a net and then in a mega-bag would likely prevent breakage and reduce melting, studies show. Other challenges, however, include turning an iceberg into potable water at its destination and environmental impacts.