Six innovative lifesavers
Air that’s drinkable
Air is not nothing. Besides nitrogen, oxygen and other gases, water in the form of water vapor is an essential constituent of air – and the amount of it that is present in air varies significantly. On average, the water vapor content in the troposphere – the lowest layer of Earth’s atmosphere – amounts to around 1.4 percent. The tropics with around three percent water vapor content in the ambient air and the poles with just around 0.1 percent are two extremes. In the quest for new drinking-water sources, researchers are now pursuing a strategy of harnessing this (invisible) humidity and have developed various technical methods for this purpose.
“Did you know that at any given time, the atmosphere contains six times more water than all the rivers on the planet together? […] Even arid desert air contains up to 40 percent humidity, especially at night.”
David Hertz, architect and inventor from California
1. Hydrogel
How it works: Scientists at the University of Texas have developed a gel that can pull drinking-water even from arid desert air using thermo-responsive cellulose – a material whose characteristics change, depending on temperatures. During cool nights, the material has the capacity to bind water. While being heated, the gel has a hydrophobic effect resulting in the release of the collected water. On balance, that’s a particularly energy-saving and easy-to-use method for any household. One kilogram (2.2 lbs) of the gel is said to cost only two euros.
Yield: In areas with relative humidity below 15 percent, one kilogram (2.2 lbs) of the gel can pull about six liters (1.6 gal) of water from air per day, according to the U.S. scientists. In humidity conditions of up to 30 percent, it’s even up to 13 liters (2.9 gal) per day. Through further optimization and thicker gel films, the amount of water can increase significantly, say the researchers.
2. Condensation
How it works: Californian inventor David Hertz’ Skywater box uses the principle of condensation: when hot air touches a cold surface water vapor liquefies. The air is heated either by solar energy or biomass. Hertz explains his invention: “We are creating a tropical climate in the box.” The process is equally simple and ingenious, enabling water to be harvested even in very dry conditions. The collected condensation is subsequently filtered and purified.
Yield: David Hertz has shown that with his boxes – small, discarded shipping containers – he can pull up to 528 gal of water from the atmosphere within 24 hours – by using 100 percent renewable energies. His formula: The higher the humidity and the hotter the temperature, the more water can be harvested and filtered. “We are CO2-negative,” says Hertz, “meaning we sequester atmospheric carbon and turn it into biochar, a soil nutrient for regenerative agriculture.”
3. Fog nets
How it works: Preferably installed in dry mountainous and coastal regions with ample fog and wind, fog collectors are vertically suspended nets consisting of a special mesh (such as nylon) that catch droplets which subsequently merge into larger drops. Without any energy input, strictly due to the force of gravity, the drops fall into a gutter, from where the fog water flows through pipes into a collection tank. Drinking water has been harvested by means of fog nets for many years and, in some cases, for decades. For instance, the WaterFoundation, an independent Munich-based organization, offers such a product named CloudFisher. Fog nets are used in Bolivia, Morocco, Peru and Tanzania, for example. Chile, Ethiopia, Spain or South Africa are suitable for fog nets as well.
Yield: The daily water yield ranges between six (1.6) and 22 liters (5.8 gal) per square meter (approx. 11 square feet) of netting, depending on the region and season. According to the Munich Re Foundation that supports projects for harvesting drinking-water in poverty-stricken regions, hundreds of thousands of people are currently benefiting from fog nets. In addition, the specialty mesh – supplemented by horizontally installed plastic panels – serves to harvest water also during monsoon periods.
Drinking-water from the ocean
The world population is growing and so is its thirst. The solution to this problem, it seems, is obvious: 70 percent of our Blue Planet Earth is covered by water. If it were possible to tap this huge supply humanity’s water problem would be solved instantly. Or perhaps not? In fact, hundreds of millions of people, worldwide, already depend on classic seawater desalination plants, while researchers are working on more profitable, sustainable and individually usable methods of removing salt from water.
4. Drinking-water at the touch of a button
How it works: Converting saltwater into drinking-water is not rocket science. However, that hasn’t been true for private citizens so far because they’d need special filters combined with powerful high-pressure pumps. That’s far too complex for the average consumer and prompted a project by a research team at the renowned Massachusetts Institute of Technology (MIT) that claims to have developed a fool-proof suitcase-like device for producing drinking-water out of saltwater – without any filters but with electric energy and at the touch of a button. The process applies an electrical field along membranes above and below a channel of water. Positively and negatively charged particles are thus repelled by the membranes while flowing past them and “filtered out.” In addition to the salt molecules, this also affects other undesirable components such as viruses and bacteria. At MIT, they call this specialized technology ion concentration polarization (ICP). In a second step, a so-called electrodialysis takes place, which removes any remaining salt ions.
Yield: The researchers expect to harvest potable water that exceeds even the quality standards of the World Health Organization (WHO). In the field, this is supposed to take barely half an hour per glass, according to MIT.
5. Desert greenhouses
How it works: In greenhouses around the globe, vegetables grow for which it’s actually too cold there. In the desert, the Norwegian NGO “Sahara Forest Project” reverses this principle to produce food crops for whose cultivation it’s actually too hot and dry. Their idea is to pump salt water into the Sahara Desert that vaporizes in greenhouses where it absorbs heat and thus cools the greenhouses. The intended final product – practically a byproduct – is clean freshwater because the vapor that condensates on the walls is collected and after another purification process becomes drinking-water. The necessary energy is supplied by solar systems. The project was initiated as far back as in 2008 and pilot projects have since been launched in Qatar and Jordan.
Yield: In an initial project phase, in which the plantations extended across an area of three hectares (7.4 acres), 10,000 liters (2,640 gal) of freshwater per day were produced by means of desalination using solar energy.
6. Drinking-water from the seafloor
How it works: A global assessment by the GEOMAR Helmholtz Centre for Ocean Research in Kiel revealed that around the globe huge freshwater reserves are hidden in the groundwater, referred to as “offshore freshened groundwater” (OFG). The crucial question is whether we can also use all these reservoirs as drinking-water sources. So far, the scientists have not been able to finally clarify which limestone rocks that store the groundwater like a sponge at a depth of down to 400 meters (1,300 feet) are already connected to land, in other words, which of them we’ve long been tapping, and which of them are not. Dr. Aaron Micallef at GEOMAR is optimistic, though: "The results we obtained so far are encouraging because we have been able to map OFG in very different geological settings and gain detailed knowledge on how it was deposited.” However, the study also identified important gaps in the scientists’ understanding of OFG such as the timing of deposition and whether recharge is currently taking place. “This information is crucial if we want to assess the potential use of OFG as an unconventional source of water,” concludes Micallef.
Yield: For the study, the research team evaluated a total of 300 documented records of OFG. They estimate the global volume of these deposits at one million cubic kilometers (240,000 cubic miles). That is about twice the volume of the Black Sea and about five percent of the estimated global volume of groundwater in the upper two kilometers (1.24 miles) of the continental crust. The deposits are mainly located in areas up to 55 kilometers (34 miles) from the respective coasts and down to a water depth of 100 meters (330 feet).
Challenges in drinking-water harvesting
Using existing drinking-water resources efficiently has to become a global sustainability goal. “Especially in the area of agriculture,” emphasizes Professor Steffen Krause from Bundeswehr University Munich. One of the focal research areas at the Chair of Sanitary Engineering and Waste Management is the supply of drinking-water: “Globally, around 70 percent of the resources that might become drinking water are used for farming. The efficiency of irrigation needs to increase in this area. In Europe, we virtually import water from regions in the world where irrigation is inefficient and where resources are excessively used, such as for cocoa, coffee or cotton.”
Another major portion of the resources that in fact are, or could become, drinking-water is lost, says Krause, because untreated wastewater is discharged into bodies of surface water and pollutes the groundwater as well. “When even surface water is contaminated due to dyeing of textiles, they should not just be used briefly as fast fashion items,” he warns. The same applies to mindful handling of food. “Foodstuffs that also account for a major part of our water footprint must no longer spoil or be disposed of to the extent that they have been so far,” says Krause.
According to Krause, solutions such as CloudFishing, hydrogels or various innovative methods for seawater desalination (see texts above) would not only assist humans in harvesting drinking-water but also benefit the environment as a whole – albeit only if negative consequential effects of the systems were avoided. A UN study in 2019, for instance, revealed that, worldwide, per day, 142 million cubic meters (5 billion cubic feet) of highly concentrated brine are discharged into the environment – far more than previously thought. That’s a serious problem because a major portion of the brine is just fed back into the ocean where it upsets the ecological balance. Krause: “The concentrates from reverse osmosis are a real problem. In some Mediterranean regions, the accumulation of the salts due to the introduction of the concentrates is already measurable.” Krause assumes that disposal of the concentrates also poses the biggest hurdle to a large-scale installation of systems in Germany as well. Another problem, he says, is the high energy requirement of desalination plants. To put things in perspective: current, commonly used osmosis desalination plants consume 7 to 7.5 kilowatt hours of electricity per cubic meter (35 cubic feet) of freshwater. Using green electricity in this area requires either an energy storage system to buffer the lulls of wind and solar energy or large water reservoirs for storing desalinated water at times when a surplus of green electricity is produced. Either variant would drive up prices.
