A Freshwater Crisis: Possible Solutions

The planet is facing a freshwater crisis, with reserves declining worldwide annually. Already, 663 million people suffer from water scarcity around the world, and roughly ⅔ of the world population experiences water scarcity for at least a month every year. In about 25 years from now, it is estimated that half the population will face water scarcity.

Some solutions right now include seawater recycling, contaminated water recycling, sewage recycling, and water production from fog. The most popular is desalination, but it comes with many problems. These include high energy consumption and horrible environmental impacts. After harvesting freshwater, it releases much saltier and warmer waste back into the ocean, and the high pressure on the water kills many microscopic organisms, such as plankton and delicate fish. It is also virtually impossible for landlocked areas or places far from water

Scientists have been trying to take inspiration from nature because it can thrive in dry weather despite being dependent on water. Some examples of this would be cacti or a Namib beetle. Cacti generally absorb and trap water droplets. A Namib beetle takes moisture from the ocean fog, and a mechanism called the Dew Bank Bottle aimed to recreate this, and was useful for nomadic people

A fairly new solution is water harvesting from the air. This includes many different methods, such as fog collection and condensation of humidity in the air. Its effectiveness is determined by relative humidity, air temperature, and total atmospheric pressure. It also requires less energy when the hygrometric degree (which measures humidity) is high. However, it isn't very efficient and requires high energy consumption when the weather isn't favorable. Natural systems have influenced the structure designs a lot, absorbing moisture at night and condensing into freshwater during the day, due to the availability of solar energy.

Water extraction/production can be split into a few main systems

• Fog collection: 

Two-dimensional vertical nets collect and condense water droplets from the fog into drinkable water. The water droplets cling to the mesh, and eventually they get too large so they fall into the collection tanks below. It doesn't require energy and can be very efficient if used properly in the right conditions. However, environmental factors dictate the productivity, so in a place where there is very little fog or humidity, it isn't super effective.

• Underground Condensation:

Surface wind pushes humid air into an underground network of pipes, and it quickly cools due to the temperature change from surface to underground. The cooling condenses the moisture and stores it in a reservoir underground. It is very cheap and affordable for rural areas, and scientists are still working on integrating solar power and improving the wind turbine structure to increase efficiency.

• Desiccants/Adsorbents:

This system uses desiccant materials or adsorbents to pull water directly from the air, similar to how a sponge works. Once the desiccant material is full, it is heated, generally using solar energy, to release clean water vapor, which can then be condensed into drinkable water. This is extremely promising, especially in dry areas, since it doesn’t need that much humidity. It also uses solar energy, which makes it sustainable, but unfortunately, it isn’t fully developed yet. Researchers are currently working on it.

• Atmospheric Water Generators 

  • Vapor Compression Method:

When water is extracted from the air, the water vapor is condensed. It consists of an evaporator, thermal expansion value, condensers, and a compressor. Circulating liquid refrigerant then gets heat from the air and reduces the temperature to below the dew point. This also turns the vapor into liquid and returns the heat to the environment. A huge drawback is that these usually use chlorofluorocarbons as refrigerants, which destroy the ozone layer. However, new commercial gases and environmentally friendly refrigerants have been developed. These systems require a lot of energy for the cooling cycle and high humidity levels, roughly 30% over the relative humidity, with a minimum 60% required.

• Peltier Effect (Electric Chip Cooling):

In this system, electricity runs through a Peltier module (thermoelectric generator), causing one side to become extremely hot and the other side to become extremely cold, causing condensation. They are small and portable, and need very little maintenance, but they have very low efficiency.

• Passive Harvestation:

In this system, surfaces that cool down naturally are left out at night so that the moisture that it collects will cool and condense. Usually, low-density polyethylene foil is used since it has hydrophilic properties and high emissivity. This means it attracts water and is good at radiating heat. It also doesn't use energy and has a simple design, making it affordable and cost-effective. It is also much more applicable than fog harvesting, since it isn’t as geographically bound. However, it only works at night and is limited by weather conditions, since those affect heat exchange. It is also affected by wind speed, temperature, relative humidity, and cloud cover. There is a lot of heat loss during this process, but the biggest negative is the low Specific Water Production. Theoretically, the maximum the dew can yield is only 0.8 kg/day/m², but the most recorded yields fall somewhere from 0.3 to 0.6 kg/day/m².

These systems are all prototypes and ideas, with scientists worldwide constantly developing new ideas and solutions.