Clean drinking water in a glass with sunlight shining in the background.

Summary

  • Some consumers find it difficult to reduce their water consumption, given the perception that water is all around us. Over 70% of the Earth’s surface is covered with water – but only about 2.5% is freshwater, and the rest is saline.
  • Around 1 in 3 people globally do not have access to clean drinking water, and this is not just in the world’s poorest regions. Water availability is a concern for many nations – even some of the most advanced ones.
  • For those living in dry climates, extracting water from the air may be the most viable solution to the water shortage. It is now possible to harvest water at 7 to 20% relative humidity – the relative midday humidity in the desert during the summer.
  • The first atmospheric water harvester with desiccant – a moisture-absorbing material – came into use in 2017. It is an off-grid, stand-alone system powered by integrated solar panels. A typical dual-panel set-up produces around 10 litres of water per day.
  • The new generation of atmosphere water capturing technology includes metal-organic frameworks (MOFs). With the introduction of solar panels and a battery, instead of relying on a single day-night cycle, the MOF can be filled and emptied up to ten cycles per hour, 24 hours per day.

Introduction

Water availability has become a significant concern all around the world. The United Nations Children’s Fund (UNICEF) and the World Health Organization (WHO) estimate that around 1 in 3 people worldwide do not have access to suitable drinking water. Waterborne diseases already account for over 50% of preventable human ailments in the world’s poorest regions. Even in some of the most advanced countries, public water supply is no longer considered safe enough to drink. This has created a billion-dollar packaged drinking water industry and plastic pollution crisis.

Many people are feeling the effects of the water crisis, and many more will be affected.  Right now, there are mainly two things we can do to mitigate the problem – conserve as much water as we can and find other sources of potable water. For those living near a large water body, all it takes is filtering the water. However, in cases where there are little to no water sources and low precipitation levels, the best option may be to harvest water from the air.

The theory of extracting water from the air may sound like something out of a science fiction movie, but experts may have found a sustainable way to achieve this with the help of solar power. It is now possible to harvest water at 7 to 20% relative humidity – the relative midday humidity in the desert during the summer. That means we may soon be extracting water from the air, even in the driest parts of the world.

Changing Attitudes Toward Water Usage

Scientists estimate that four billion people live in regions with severe freshwater shortages for at least one month each year.

In 2018, Cape Town (South Africa) headed into its fourth consecutive year of drought, facing the risk of “Day Zero” – when water supply would be cut off due to the severe water shortage. Residents were warned that they would have to collect water from 200 planned centralized water centres if the taps were turned off. Following the official announcement on the risk of running out of water, there was a steep drop in consumption and bans were put on filling swimming pools and washing cars. However, quotas on agricultural water usage and the return of much-needed rain are what allowed Cape Town to dodge Day Zero.

While Cape Town nearly became the first major city to run out of water, other major cities – including London – face a similar fate. The UK Environment Agency has warned that London, and the rest of southeast England, will not have sufficient water supplies by 2050 unless water-wasting habits change.

Scientists estimate that four billion people live in regions with severe freshwater shortages for at least one month each year. By 2050, this number is estimated to increase to between 4.8 billion and 5.7 billion. The reasons for this include climate change, polluted water supplies and rising demand due to both population growth and changes in usage.

It is challenging to persuade consumers to reduce their water consumption, given the perception that water is all around us. Over 70% of the Earth’s surface is covered with water – but only about 2.5% of that is freshwater, and the rest is saline. In addition, the majority of freshwater is locked in ice caps, glaciers and permanent snow. Out of all this water, less than 1% of the Earth’s water is available for drinking.

The race to find technical solutions to mitigate the looming water crisis is underway. There is a boon in desalination plants that strip salt from seawater. However, another lesser-known family of technologies known as atmospheric water harvesters is growing in popularity. As the name suggests, the technology involves capturing water from the atmosphere, including gaseous water (vapour) and liquid water (droplets) from the air around us.

Atmosphere Water Capturing Technology

The majority of the atmospheric water harvesters mimic how dew forms on vegetation early in the mornings and how condensation forms on cool items when we take them out of the fridge.

The technology to capture water vapour from the atmosphere has been around for over two decades, and many companies sell devices that do exactly that. Although water harvesting technology has been available for some time now, the market is still tiny. The limited market growth is due to the high initial investment cost and the high energy consumption. Another issue is water capture inefficiency – especially in dry, desert conditions where water harvesting technology may be required the most.

Atmospheric water harvesters are currently being used during military operations in remote, drought-struck regions, disaster relief efforts, or where local drinking water supplies have been contaminated. In addition, some remote holiday resorts with limited freshwater supplies sometimes use atmospheric water harvesters.

The majority of the atmospheric water harvesters mimic how dew forms on vegetation early in the mornings and how condensation forms on items when we take them out of the fridge. When warm air gets into contact with a cold surface, it is rapidly cooled. If the surface is below a specific temperature – the dew point – the water vapour in that air condenses to a liquid phase. It is then possible to collect the resulting water droplets that form on the surface.

Condensation against a cooler, coiled surface is the most established water vapour harvesting technology, but an alternative approach is starting to gain traction – using a desiccant. Compared with condenser-based technology, air-water harvesting technology has lower energy consumption and higher water extraction efficiency when desiccants are used. In addition, desiccant-based water harvesting is the best way to achieve air-water harvesting in arid or desert regions.

Desiccants are hygroscopic materials that suck up moisture like a sponge. There are some desiccants found in everyday products that you may be familiar with. For example, the absorbent layer in baby nappies containing sodium polyacrylate and silica gel sachets in various goods’ packaging. Desiccants, like lithium chloride solutions and silica gels, are also used in some commercially available dehumidifiers.

In 2017, the first atmospheric water harvester with desiccant reached Source, a tech marketplace. The harvester is an off-grid, stand-alone system powered by integrated solar panels. A typical dual-panel set-up produces around 10 litres of water per day. The volume of water varies depending on humidity levels and hours of sunlight. To date, the hydro panel has been installed in more than 35 countries.

There is now a much larger atmospheric water harvester containing a liquid desiccant called the Drupps Concept. The prototype is located at the company’s headquarters in Uppsala, Sweden. It is estimated to produce 3,000 litres of water per day. The set-up is modular, so additional desiccant modules can be added in drier climates or when more water is needed.

Solar Power Supporting the Next Generation of Desiccants

With the introduction of solar panels and a battery, instead of relying on a single day-night cycle, the MOF can be filled and emptied up to ten cycles per hour, 24 hours per day.

A ball and stick model of a metal-organic framework.
The next-generation desiccants are being explored for atmospheric water harvesting purposes. This includes composite sorbents, such as the activated carbon–lithium chloride and metal-organic frameworks (MOFs). The use of MOFs for water capture started in a chemistry laboratory at the University of California and is now being carried forward by a spin-out company called Water Harvesting.

MOFs have substantial internal surface areas – meaning they can hold significant amounts of water in their pores. In addition, there is a cooperative result when they are used to capture water. The first water molecules gather together to form seeds onto which other water molecules then bind. So you start with low water uptake, and it substantially increases before levelling off once the pores are fully packed.

There have been many prototypes for MOF water harvesting technology tested in both the Mojave and Arizona deserts. The initial prototype was a basic plastic box-within-a-box structure. The internal box holding the MOF is opened to the air overnight. The MOF absorbs water, and then the device closes during the day. The desert sun heats the box, and water condenses on the inside walls of the outer box due to the temperature difference between the box and the outside environment.

The initial design produced between 200 to 300 millilitres of water per kilogram of MOF, depending on the atmospheric humidity levels. Scientists have made a few adjustments to increase the volume of water produced per kilogram of material, including incorporating solar panels. Solar panels generate electricity that can power small fans to push air inside the MOF. When the time is right, they heat the MOF to speed up condensation. Fortunately, the energy needed for this process is pretty low as the water is not bound tightly into the pore.

With the introduction of solar panels and a battery, instead of relying on a single day-night cycle, the MOF can be filled and emptied up to ten cycles per hour, 24 hours per day. As a result, the team working on this project is approaching a magnitude increase in the volume of water collected per kilo per day.

It’s not only large-scale devices being developed for water harvesting. Some small kitchen countertop harvesters are in the works. These small-scale devices will produce enough drinking water for a household. With the help of solar, large-scale devices will one day collect water for industrial use and even supply clean drinking water to remote communities.

Closing Thoughts

Water-from-air technologies may help tackle the drought crisis but not on their own. It is more likely that they will be part of a multifaceted approach to addressing water scarcity in the future. There looks to be no stand-alone solution, so other technologies and improved water conservation and distribution systems are needed. Nevertheless, the continued advancement of devices that pull water from the air shows promise. With renewable energy providing the power, the thirstiest parts of the world may soon be a little less at risk of drought.

Frequently Asked Questions (FAQs)

Can you produce water from air without electricity?

Yes, it is possible to produce water from the air without electricity. A metal-organic framework (MOF) with a zirconium element can capture water from the air at night, store it, then release it during the daytime upon exposure to the heat of sunlight. Without electricity, the natural day-night cycle is relied upon, so there is limited water production.

 

What is considered safe drinking water?

Drinking water, also known as potable water, comes from surface and ground sources and meets safe consumption standards. Before drinking, water from natural sources should be treated for microorganisms, toxic chemicals, viruses, bacteria, and fecal matter.

 

What is a desiccant?

A desiccant is a substance that absorbs water. It is most commonly used to remove humidity that would normally degrade or destroy products sensitive to moisture. Scientists are now looking into ways desiccant technologies can extract water from the atmosphere and use it for drinking.

 

How do MOFs work?

MOFs are organic-inorganic hybrid crystalline porous materials consisting of a regular array of positively charged metal ions surrounded by organic linker molecules. The metal ions create connections that bind the arms of the linkers together to create a repeating, cage-like structure.

 

Can solar power produce water?

Solar power is being used to boost water production of water harvesting devices that harvest water from the air. Depending on the climate, hydro panels can produce up to 5 litres of clean drinking water on a typical day. In addition, solar power and battery technology have significantly boosted water production as they no longer rely on a single day-night cycle – the devices can be filled and emptied up to ten cycles per hour, 24 hours per day.

 

Westbridge Energy Corporation

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