by Udo Pollmer

Wherever people live, clean drinking water is needed, and not in short supply. With the vast amounts of water that are consumed, it is easy to get the impression that we will eventually run out. 

The German Federal Environment Agency knows how to address these fears: "In the future ... more groups of users than today will compete for an increasingly scarce resource. Therefore, we have to think about a fair distribution in case of prolonged drought, i.e. about a prioritisation that...

...also takes into account the needs of the (water) ecosystems".¹ The choice of words reveals that someone is fishing in the dark here. Which users would want to see their needs prioritised in water bodies within the framework of "equitable distribution"? Toads, mosquitoes, fish tapeworms?  

The journalist Franz Alt recently called for "Germany needs a water emergency plan" and "a water turnaround".² Water shortages are a typical consequence of a lack of "climate justice". The churches are using the opportunity to trade in ecumenical indulgences: "The climate collection is a CO2 compensation fund of Christian churches, through which ... every congregation can compensate for unavoidable emissions from" - well, what? - from "printed matter".³ From the church's point of view, the world is not perishing from blasphemy a la gender and Gomorrah, but from the Bible, catechism and hymnal - because they pollute the environment during their production.

A look at the statistics clarifies the situation: According to Statista, the consumption of available water in Germany has fallen continuously from 25 % in 1991 to 12.5 % in 2016, i.e. to half.⁴ If the UBA's figures are correct, then it is once again less in the meantime.⁵³ So this is supposed to be the water emergency that has concerned officials croaking for "fair distribution"?
We will soon see why water consumption in Germany has fallen drastically. But before that, let's take a look at the global situation. 

No need to worry 

The fatalistic impression that humans cannot use the inexhaustible supply of salt water or can only do so with enormous energy expenditure is nonsense. Decades ago, the oil states in the Middle East actually paid a lot for their seawater distillate. The necessary energy was supplied by waste heat from power plants. In the meantime, sun and wind are also available on the sea coasts. Today, new processes such as evaporation in a gravitationally supported vacuum make it possible to produce inexpensive fresh water from salt and brackish water at low temperatures. ^5,6

Almost as much fresh water as distillation is now supplied by reverse osmosis. Here, the seawater is pressed through fine membranes that retain the salt.⁷ This saves energy compared to distillation, but has the disadvantage that the membranes become germinated and clogged. They have to be cleaned regularly with disinfectants and antiscalants.⁸ Worldwide, the 17,000 desalination plants supply almost 100 million cubic metres of drinking water every day.⁹ And it is quickly becoming more: novel nano-materials such as graphene accelerate evaporation even more through capillary effects.¹²

Graphene also solves the problem of germy membranes: it has an antibiotic effect. Nanotubes and quantum dots also prevent fouling, i.e. the formation of biofilms.^10,11 Graphene tubes are also tear-resistant, wafer-thin and smooth on the inside. This not only prolongs the life span, but also increases the performance so much that the maximum yield allowed by molecular dynamics calculations is now exceeded by the material by a power of ten.¹³

Everything against thirst

For decades, drinking water can be produced almost anywhere where water of any quality is available. Everything has been available up to now, from large systems to handy devices for your jacket pocket. The smallest ones resemble thick straws (Lifestraw™).³⁸ You dip them into a puddle and - suck in drinking water. The ultrafiltration unit removes all bacteria, viruses and parasites, dirt particles anyway. One "straw" delivers ten thousand litres and more. 

There are also inexpensive systems for families. They provide clean water for years at any location and without external energy. It is freshly produced as needed and does not bob around in tanks where algae have a rendezvous.¹⁸ Here are a few examples of the many technical solutions available:

• One of the first compact systems was the Rosendahl collector.²⁹ It produces drinking water directly from almost any raw water, including salt water; between 5 litres a day and 75 cubic metres, depending on the design. The collector can be produced anywhere, it can be used decentrally thanks to the PV system, it requires no chemicals and is almost maintenance-free. A disadvantage is the complex control system that adjusts the raw water inflow to the respective solar radiation.
• Relatively new is the SkyHydrant™, whose inner workings consist of inexpensive hair-thin membranes. Even small devices weighing 13 kilos provide 5,000 litres of clean drinking water daily. The technology is particularly suitable for groundwater and river water. The necessary negative pressure for the water to flow through the filter is generated by gravity. The systems run almost maintenance-free, the membrane only needs to be replaced after 10 years. The SkyHydrant™ requires neither external energy nor chemicals. ^15,16
• Inline electrolysis is also used decentrally. It uses the disinfecting effect of chlorine - but without adding chlorine. This is because there are always a few chloride ions dissolved in natural water anyway. With a little electric current - generated by photovoltaics - a disinfectant is formed.^17,18 The water is then always germ-free - and even contains fewer chlorine atoms than before.
• In the tropics and subtropics, the sun can also be used directly to produce drinking water without converting it into electricity (Solar Water Disinfection, SODIS). Used PET bottles are filled with water and exposed to the midday sun for about 6 hours. The UV radiation kills bacteria, viruses and parasites, the infrared radiation supports this by heating.^19,20 There is no cheaper way to tame germs. If you want to be on the safe side and can afford it, you can also operate a UV-C lamp with photovoltaics.²¹ An addition of pre-treated rapeseed pollen and plasmonic nanoparticles has a similar effect.^22,23,32 Others add nanowires of titanium dioxide to destroy pesticides and medicines by sunlight at the same time.²⁴ In the meantime, the so-called bottle reactors have progressed so far that their principle is being considered for continuous drinking water treatment. ²⁵
• If water is available locally, drinking water can also be produced by bicycle: a device called CycloClean™ is mounted on the back of a bike. The water is taken from bodies of water or swimming pools and pumped through several filters by pedal. This produces six litres of clean drinking water per minute.²⁶ Cycloclean is offered to self-suppliers in countries like India or Bangladesh. Only seawater cannot be desalinated with it. 
• There is no shortage of simple and useful inventions. For example, the Hippo Roller, popular in southern Africa: a plastic barrel made of UV-stable polyethylene with a capacity of 90 litres is rolled on a pole like a lawn roller.^27,28 This means that children and women no longer have to carry the water home on their heads from distant water points. Filters can be placed inside the barrel so that the contents arrive at their destination purified.
• The simplest devices need neither electricity, nor chemicals, nor technology like the Watercone®. Take a plastic bonnet made of polycarbonate, put it over a bowl of salt water and wait until the sun's rays have evaporated the water. This water collects in a channel on the inner edge. A canopy with a diameter of 60 cm provides 1.5 litres of drinking water per day. If the Watercone is placed directly on the ground, soil moisture can be obtained.²⁹

For some regions in the third world, even this unpretentious technology is too expensive. A simple Watercone® including transport costs about 20 euros. The crystal-clear polycarbonate gradually loses its transparency, and with a maximum lifespan of 5 years, this amounts to 1 to 2 cents per litre. Therefore, attempts were made to purify drinking water with locally available, cheap materials.³⁰

In the process, methods that were once common in Europe are being used. Sand, gravel, shells and activated charcoal, e.g. from coconut shells or bamboo, serve as filters. Activated charcoal absorbs natural and anthropogenic pollutants. The filter material is filled individually into barrels through which the water flows in a cascade. The heart of the system is a barrel full of sand into which steel wool has been placed. Steel wool disinfects.³⁰ If all else fails, a PET bottle without a bottom will do. Turn it upside down and fill it with the above-mentioned materials in layers. ³¹

Taken from the air: Water in the desert

All these methods presuppose that water is available. But even in dry but misty mountainous areas of Ethiopia or India, it is possible to harvest drinking water even if there is no water flowing anywhere.³⁹ So-called warka towers, scaffolds made of wood or bamboo, are covered with close-meshed plastic nets. The mist is deposited in these and flows together to form larger drops. Such a tower supplies up to 400 litres of water a day.⁴⁰

In the Moroccan desert, the dew is harvested with large polypropylene nets stretched on frames. Up to 10 litres per square metre flow out per day.^41-43 Laboratory tests suggest that optimised design of the net surface will lead to much higher yields.^44-45 This ensures a supply of drinking water for the population of sparsely populated areas. 

The wind towers in Ethiopia and the nets in Morocco point to our greatest source of fresh water: The air. In principle, the extraction of humidity is nothing new, even in our latitudes; it also works without fog or dew. For this purpose, the air is cooled like in an air conditioner until the water condenses. The lower the humidity, the more cooling is required and the more electricity is consumed. In our climate, appliances the size of a refrigerator supply 20 litres a day.⁴⁶ In dry areas, where water is more urgently needed, they are useless. 

The breakthrough: MOF

But the days of capacitor devices are numbered. New materials increase the effectiveness by orders of magnitude. This means that a new era is beginning here, too. In addition to the hydrogels already mentioned, the focus is on metal-organic frameworks, so-called MOFs: Metal Organic Frameworks, crystalline porous materials e.g. made of zirconium, cross-linked by compounds such as fumaric acid. ⁴⁷

MOFs soak up liquid. Even in cold salt deserts like the Atacama, far drier than Death Valley, water can still be extracted with it.^51,54 In the Saudi capital Riyadh, a kilo of powder harvests a whopping 30 litres a day in dust-dry August. The water is absorbed during the cooler night and desorbed during the day by sunlight or heat.^48-50

"With MOF water harvesting devices," says their inventor Omar Yaghi, "we not only have the potential to provide clean water in any climate and any season, but also to make water supply decentralised and mobile." "In the foreseeable future, MOF water harvesting systems will serve to make water a human right."⁵¹ Clean drinking water in any quantity, whether in the desert or in the mountains, by the sea or in the cold steppes. Currently, Yaghi is working on devices that supply 20,000 litres a day for an entire village with a PV system.⁵¹

The consequences of the technological breakthrough are hardly foreseeable. This will make the treatment of groundwater or seawater, which has been common up to now, uneconomical in many cases. Many an environmental discussion and the grumbling of the NGOs will probably have come to an end. The total amount of water in the air is estimated at about 13,000 cubic kilometres.⁴³ The supply in the atmosphere is inexhaustible, it is constantly replenished by evaporation, especially over the oceans. Every day, more than 1000 km3 are added.⁵² A good reason for more serenity.

Sanitary towels as pioneers 

One of the first starting points for the development of such materials was the goo that jellyfish are made of. It initially served as a model for the hydrogels in sanitary pads. When dry, they absorb liquid and remain dry on the outside, so nothing leaks out. Then followed gels that additionally release water as if on command through changes in temperature or pH, through UV light or electric fields.^33,34 But it was nano technology that opened the door to water treatment.³⁵

This is where the hierarchical nanostructured gels (HNG) made of polyvinyl alcohol and graphene oxide come into play.³² They absorb any water, whether from salt or dirty water, transport the pure water upwards in their nano-capillaries via surface effects, absorb sunlight, convert it into heat at the top with an efficiency of 90 %, lower the enthalpy of the water and evaporate the fresh water in record time by means of a nanoscale rough surface.^14,35 In the meantime, it has been possible to produce such special gels by template-supported self-assembling, the nanoscale starting materials sorting themselves independently into the right place of a matrix. This allows mass production of elastic hydrogel evaporators.^36,37 Here, too, the fascinating possibilities have not yet been exhausted.

Brainwashing via water-saving button

What remains is the concern about water pollution. For most citizens, "industry" is the bad guy. Worldwide, it uses about 20 per cent of fresh water. In Germany it is less, and this is mainly used as cooling water. In Europe, it usually has to clean and treat its production waste water. But in emerging countries like China, where the number of industrial plants is growing fast, factory waste water is disposed of untreated in rivers and lakes. 

Today, local companies usually recycle their process water; only the waste water from sanitary facilities still flows into the sewage system. In the past, the process water was purified with membrane separation processes and ion exchangers, today mostly by vacuum distillation. If necessary, industry-specific pollutants can be specifically separated by membrane absorbers and destroyed by electrolysis or plasmalysis.⁵⁵ As a result, our water consumption has dropped considerably.

To get an idea of the technical state of the art, the difficult process waters of the galvanic and plastics industries are mentioned: Treatment begins with pulsed electric fields to remove oils, followed by electrophysical precipitation to separate the metals, which are then recovered by electrodialysis. The by-product is hydrogen, which provides energy for a fuel cell. After electrooxidation to destroy any remaining pollutants, the salts are separated by capacitive deionisation. The result is highly pure water, obtained without the addition of chemicals. ⁵⁵
Today, any wastewater can be treated - treated to make drinking water. And as often as desired. Fortunately, the effort required for industrial wastewater is usually manageable, since we know exactly which substances end up in the waste water. Urban waste water is more complex. Due to the almost infinite number of ingredients in body care products, cleaning agents and medicines, many a single household discharges more questionable chemicals into the sewage treatment plant than a company of pigs in a fully occupied fattening plant. 

Of course, hydrogels and MOFs are not only suitable for obtaining drinking water, but also for treating waste water⁶⁴: "These materials offer an extraordinarily large surface area, mechanical resistance, atomic thickness, nanoscale pores and reactivity to polar and non-polar water pollutants. These properties give them high selectivity ... providing excellent efficiency in water purification."¹³ And once again, a pressing problem of humanity is solved - and no one noticed. 

Meanwhile, our society is sliding into dementia. Franz Alt is my chief witness: we must save water, he writes, "the Bundestag should pass a law that prescribes the installation of economical fittings and promotes water saving toilets, water saving showers, water saving washing machines and water saving dishwashers".⁵⁶ How crazy! Thanks to water-saving measures in the household, the sewers have to be flushed regularly with fresh drinking water. They are technically designed for the amount of water required for adequate household hygiene.

As if in mockery, the fug rises from the manhole covers in summer because the sewers are no longer flushed properly. Now the public utilities pump fresh water into them. In Berlin alone, up to half a million cubic metres of treated drinking water rush through the sewers on some days.⁵⁷ Saving water in the household does not affect water consumption in Germany. We have enough water, but too little sense.

Agriculture: the big hoax

No crops without water. The WWF knows the danger. According to an educational pamphlet for the German Michel [i.e. a German nickname, standing for the embodiment of the good-natured, naive, narrow-minded German], agriculture "consumes" 70% of the water.⁵⁸ What the WWF does not mention is that, - according to the UBA - "irrigated agriculture is only of minor importance in Germany, with a water withdrawal of about 1.3 percent of the total withdrawal volume".¹ So again propaganda that has turned many young people against our farmers.

It gets even worse: for climate priests like Franz Alt, the reason to post that 15,000 litres of water are needed for one kilo of beef.² A whole bull of over 1000 kg slaughter weight needs millions of litres, whole swimming pools. To make this claim, climate activists have, for example, added up the rain that falls in wet years on the meadows where animals graze and thrive, and dubbed this rain "consumption". ⁵⁹

You have to let this logic roll off your tongue: When it rains, grass grows. Grass consumes water and that's how drought comes about. With this mathematics, the oceans can be dried up by aquaculture. Even the hard-headed WWF has realised by now that animal foods consume the least water.¹ In order to produce vegetables - which our health eaters like to let rot after buying them - plenty of water is needed, not only in the dust-dry south of Spain. Although we have to import the vast majority of fruit and vegetables, a vegetarian diet helps save water, according to Franz Alt.²

In many greenhouses, water has long since flowed through hydroponic circulation systems, i.e. through pipes in which the roots of the plants are supplied with water, fertilizer and plant protection. Nothing can seep away any more, all water is recycled and reused. Nevertheless, cultivation is anything but water-neutral, because vegetables consist to a large extent of water, e.g. 97 percent of cucumbers. This has to be replaced, as does evaporation through the leaves. In this respect, the water-saving effect of hydroponic greenhouses for vegetables is rather meagre.⁶⁰

Conclusion: An environmentalist would quench his thirst without the diversions via a Spanish greenhouse. Those who fear a lack of water are happy to forego asparagus, lettuce and other leafy vegetables of low nutritional value and high water content. They reach for hamburgers and chips, pork loin on cabbage, Thuringian dumplings with roulades or fried potatoes with scrambled eggs. Because animal products are produced here with fodder that thrives without any irrigation: grass, maize, feed barley. Or with inedible residues from the processing of vegetable raw materials such as bran, expeller from oilseeds or glycerine from biodiesel production. ⁵⁹

Gone with the Wind

Of course, there are regions on this earth that have come or will come to the brink of the abyss due to improper use of their resources.⁶⁷ The Aral Sea is probably the best-known example. Once the Soviet leadership had decided to establish cotton collective farms and for this purpose they diverted the inflows of the lake to the fields. The lake degenerated into a salt desert. ⁶⁸
In north-eastern China, artificial irrigation made a second harvest a year possible. But after half a century, the situation is becoming critical: the aquifers have sunk alarmingly - by up to 50 metres. At the same time, saltwater is seeping into the depleting layers in coastal areas. 

Or in India: In the Indus plains, pumping costs have risen massively due to the declining groundwater. However, since electricity for pumping is almost free, the farmers still see no reason to use this resource more prudently.^65,66,69

Example Volga delta and adjacent semi-deserts: Due to the high evaporation of early potato, vegetable and melon crops, irrigation is abundant with river water, the fields are ploughed despite a thin humus layer and thus the structure of the soil is damaged. Due to the low cation exchange capacity of the soil, this, together with the natural load of calcium, magnesium and sodium in the water, leads to salinisation in the long term. Around the salt lakes that form, only the cultivation of sea asparagus (Salicornia) then succeeds. 

In Germany, farmers are resorting to "self-help" to dry out their fields: they are relying on wind farms. Their wake vortices have an effect over 50 kilometres inland, especially at night, when the propellers whirl the cool moist air from the ground upwards, and in return transport warmer air from a higher altitude to the ground. This raises the temperature on the field, and the soil moisture is blown away by the turbulence.^61,62 A hot summer quickly turns into a great drought. So it does exist: the man-made climate catastrophe - through climate protection.

The desert grows - no longer

The cardinal proof that the world is not dying of thirst and starvation through constant desertification was provided by the states in the Gulf: they transformed sandy deserts into a Garden of Eden. Green wherever the eye looks, thousands and thousands of square kilometres. Everywhere fruit plantations, vegetable fields and lush meadows. Fifty years ago, there was nothing here but sand. Today, the newly created plantations supply the megacity Abu Dhabi with fresh fruit and vegetables.⁶³

The sheikhs planted hundreds of millions of trees, whose roots are supplied with vital water directly and sparingly from hoses via drip irrigation. Irrigation with desalinated seawater has changed the climate; it now rains more often in the Persian Gulf, which benefits the vegetation.⁶³ It may be that a gigantic scientific and technical effort was necessary for this, as well as enormous financial resources. 

Today, with the new materials, techniques and experience, the effort would be manageable. Water-storing hydrogels, in this case made of polyisopropylacrylamide and a photothermal converter, are an option here.³⁵ They can be used not only to green deserts, but also to irrigate fields and fields of crops. As soil mats, they extract humidity at night and release it in doses to the crops during the day, stimulated by daylight. These "self-watering soils" also have what it takes to revolutionise agriculture.³⁵

As humanity embarks on this new world, we fear we will all have to die of thirst and starvation if we do not bow to the demand for a carbon tax for more "climate justice", whatever that may be. But the climate cannot be an object of justice. Those who are nevertheless concerned about water should take Omar Yaghi, the inventor of the MOF, as an example: fresh drinking water will not become a human right through climate collections or climate taxes, but through intelligent technology that is made available to all people.

References

1. UBA: Trockenheit in Deutschland – Fragen und Antworten. 15. Juli 2022

2. Alt F: Deutschland braucht einen Wasser-Notfallplan. Klimareporter 31. Juli 2022

3. Klima-Kollekte: kirchlicher Kompensationsfonds. Klima-Kollekte.de

4. Statista: Wassernutzungs-Index für Deutschland bis 2016. De.statista.com 2022

5. Zheng H: Solar Energy Desalination Technology. Elsevier, Amsterdam 2017

6. Chang H et al: Evaluating the performance of gravity-driven membrane filtration as desalination pretreatment of shale gas flowback and produced water. Journal of Membrane Science 2019; 587: e117187

7. Hoek EMV et al: Sustainable Desalination and Water Reuse. Morgan & Claypool 2021

8. Melnik L et al: Antiscalants in the process of reverse osmosis: antiscaling mechanism and modern problems of application. Water Treatment and Demineralization Technology 2021; 42: 450-464

9. Saadat AHM et al: Desalination technologies for developing countries. Journal of Scientific Research 2018; 10: 77-97

10. Zhou X et al: A hydrogel-based antifouling solar evaporator for highly efficient water desalination. Energy & Environmental Science 2018; 11: 1985-1992

11. Diez-Pascual AM: State of the art in the antibacterial and antiviral applications of carbon-based polymeric nanocomposites. International Journal of Molecular Sciences 2021; 22: e10511

12. Salehi AA et al: Hydrogel materials as an emerging platform for desalination and the production of purified water. Separation & Purification Reviews 2021; 50: 380-399

13. Homaeigohar S, Elbahri M: Graphene membranes for water desalination. NPG Asia Materials 2017; 9: e427

14. Zhou X et al: Hydrogels as an emerging material platform for solar water purification. Accounts of Chemical Research 2019; 52: 3244-3253

15. Dieterich J: Eine Quelle der Hoffnung. Brand eins https://www.brandeins.de/corporate-services/impulse/eine-quelle-der-hoffnung

16. Peter-Varbanets M et al: Gravity driven membrane disinfection for household drinking water treatment. 35th WEDC International Conference, Loughborough 2011

17. Landmark M et al: Passive in-line chlorination for drinking water disinfection: a critical review. Environmental Science & Technology 2022; 56: 9164-9181

18. Otter P, Goldmaier A: Solar- und Wassertechnik ermöglichen neue Lösungsansätze für die Trinkwasserproblematik in Entwicklungsländern. Deutsche Lebensmittel-Rundschau 2014; 110: 54-59

19. Juvakoski A et al: Solar disinfection – An appropriate water treatment method to inactivate faecal bacteria in cold climates. Science of the Total Environment 2022; 827: e154086

20. Strauss A et al: Comparative analysis of solar pasteurization versus solar disinfection for the treatment of harvested rainwater. BMC Microbiology 2016; 16: e289

21. Chauque BJM et al: Development of solar water disinfection systems for large-scale public supply, state of the art, improvements and paths to the future – a systematic review. Journal of Environmental Chemical Engineering 2022; 10: e107887

22. Xia D et al: A modified flower pollen-based photothermocatalytic process for enhanced solar water disinfection: photoelectric effect and bactericidal mechanisms. Water Research 2022; 217: e118423

23. Tang Z et al: Nanomaterial-enabled photothermal-based solar water disinfection processes: fundamentals, recent advances, and mechanisms. Journal of Hazardous Materials 2022; 437: e129373

24. Horvath E et al: Solar water purification with photocatalytic nanocomposite filter based on TiO2 nanowires and carbon nanotubes. npj Clean Water 2022; 5: e10

25. Chaúque BJM, Rott MB: Solar disinfection (SODIS) technologies as alternative for large-scale public drinking water supply: advances and challenges. Chemosphere 2021; 281: e130754

26. Nippon Basic Co. Ltd: New Cycloclean: Compact portable distribution type purification plant and environmental education. https://eri-kawasaki.jp/english/wp-content/uploads/2019/02/6606b636b7c05cb6147f986fd34b283f.pdf

27. Reichel R, Wu N: Water Transport System for Rural Africa. McGill University, Report 2011

28. Moldan N: Imvubu’s hippo water roller facilitates water access in rural African communities. RotoWorld 2010; 6: 28-32

29. Augsten E: Desalination by means of wind and sun. Sun & Wind Energy 2007; (2): 32-36

30. Huang Z et al: Universal access to safe drinking water: Escaping the traps of non-frugal technologies. Sustainability 2021; 13: e9645

31. Singh AK et al: A review of low cost alternative of water treatment in rural area. 10th all India peoples’ technology congress at: Kolkata on 6th – 7th February 2015

32. Zhao F et al: Highly efficient solar vapor generation via hierarchically nanoconstructed gels. Nature Nanotechnology 2018; 13: 489-495

33. Nicolella P et al: Reversible hydrogels with switchable diffusive permeability. Macromolecular Chemistry & Physics 2021; 222: e2100076

34. Li CY: Spontaneous and rapid electro-actuated snapping of constrained polyelectrolyte hydrogels. Science Advances 2022; 8: eabm9608

35. Guo Y et al: Multifunctional hydrogels for sustainable energy and environment. Polymer International 2021; 70: 1425-1432

36. Guo Y et al: Highly elastic interconnected porous hydrogels through self-assembled templating for solar water purification. Angewandte Chemie, International Edition 2022; 61: e202114074

37. Xu J et al: Ultrahigh solar-driven atmospheric water production enabled by scalable rapid-cycling water harvester with vertically aligned nanocomposite sorbent. Energy & Environmental Science 2021; 14: 5979–5994

38. Norton GJ et al: Physical measures to reduce exposure to tap water-associated nontuberculous Mycobacteria. Frontiers in Public Health 2020; 8: e190

39. Bhushan B: Design of water harvesting towers and projections for water collection from fog and condensation. Philosophical Transactions Royal Society A 2020; 378: e20190440

40. Mishra SS: Warka water tower: an innovative method of water harvesting form thin air in semi-arid regions. International Journal of Scientific Engineering and Research 2018; 7: (1)

41. Dodson LL, Bargach J: Harvesting fresh water from fog in rural Morocco: research and impact Dar Si Hmad’s Fogwater Project in Ait Baamrane. Procedia Engineering 2015; 107: 186-193

42. Jarimi H et al: Review of sustainable methods for atmospheric water harvesting. International Journal of Low-Carbon Technologies 2020; 15: 253-276

43. Qadir M et al: Fog water collection: Challenges beyond technology. Water 2018; 10: e372

44. Zhang M et al: Diversifying water sources with atmospheric water harvesting to enhance water supply resilience. Sustainability 2022; 14: e7783

45. Kim JY et al: Improvement of water harvesting performance through collector modification in industrial cooling tower. Scientific Reports 2022; 12: e4658

46. Schomäcker S: Tolle Idee! Was wurde daraus? – Trinkwasser aus der Luft. Deutschlandfunk 26. Juli 2022

47. Kim H et al: Water harvesting from air with metal-organic framework powered by natural sunlight. Science 2017; 356: 430–434

48. Hanikel N et al: MOF water harvesters. Nature Nanotechnology 2020; 15: 348-355

49. Hanikel N et al: Evolution of water structures in metal-organic frameworks for improved atmospheric water harvesting. Science 2021; 374: 454–459

50. Biswas RN: Water harvesting from desert air using MOF and sunlight. International Journal of Pollution and Noise Control 2022; 8: 13-24

51. Xu W, Yaghi OM: Metal-organic frameworks for water harvesting from air, anywhere, anytime. ACS Central Science 2020; 6: 1348-1354

52. La Rivière JWM: Threats to the world's water. Scientific American 1989; 261 (No. 3): 80-97

53. UBA: Wasserressourcen und ihre Nutzung. Umweltbundesamt.de vom 14.11.2022

54. Fathieh F et al: Practical water production from desert air. Science Advances 2018; 4: eaat3198

55. Fraunhofer IGB: Aufbereitung und Reinigung von Prozesswasser ressourcen- und energieeffizient. Stuttgart o.J. 

56. Alt F: Dringend nötig: Ein Wasser-Notfallplan für Deutschland. Telepolis 31. Juli 2022, Heise.de

57. Neubacher A: Deutschland, ein Ökomärchen. Der Spiegel 2012; H.11: 60-64

58. WWF Deutschland: Wasserverbrauch und Wasserknappheit. Berlin 2021

59. Pollmer U et al: Don’t go veggie! Hirzel, Stuttgart 2017

60. Nikolaou G et al: Energy and water related parameters in tomato and cucumber greenhouse crops in semiarid Mediterranean regions. a review, part ii: irrigation and fertigation. Horticulturae 2021; 7: e548

61. Miller LM, Keith DW: Climatic impacts of wind power. Joule 2018; 2: 1–15

62. Platis A et al: First in situ evidence of wakes in the far field behind offshore wind farms. Scientific Reports 2018; 8: e2163

63. Douglas H: Das CO2 und die grüne Welt. Tichys Einblick, 6. Mai 2016

64. Erakovic Z, Stefanovic D: Purification of contaminated wastewater with the help of graphene composites with hydrogels. Facta Universitatis, Working and Living Environmental Protection 2022; 19: 27-36

65. Bhattarai N et al: The impact of groundwater depletion on agricultural production in India. Environmental Research Letters 2021; 16: e085003

66. Fischer C et al: Groundwater irrigation reduces overall poverty but increases socioeconomic vulnerability in a semiarid region of southern India. Scientific Reports 2022; 12: e8850

67. Wada Y et al: Global depletion of groundwater resources. Geophysical Research Letters 2010; 37: L20402

68. Synnott M: Zentralasien – Es war einmal ein See. National Geographic 2015; H.6: 138-153

69. Pengra B: A glass half empty: Regions at risk due to groundwater depletion. UNEP Global Environmental Alert Service, January 2012

Copyright: EU.L.E. e.V.
Originally published in December 2022 => Pollmers Mahlzeit: WASSER - Teil 3: Trinken bis zum Abwinken

English editor: Josef Hueber, Eichstätt