Here’s a little-known fact. The atmosphere we breathe holds 200,000 trillion liters of water in vapor form. If we put all of it into a 1x1 km column, it would reach halfway to the moon.
Assuming healthy humans need 1 liter of pure drinking water per day, daily drinking water consumption needs for the world’s 8 billion people could be met using only 0.000004% of the water vapor contained in the atmosphere.
In other words, water vapor is sufficient for 25 million times the Earth’s population. Given that the residence time of a water molecule in the lower atmosphere is 9-10 days, the atmosphere has more than 2 million times enough water to provide the world’s entire population.
The challenge is finding an affordable device to make that water vapor readily available in liquid form to the people who need it most – those that might rely on bottled water or otherwise don’t have reliable piped water supplies.
Enter a new technology—atmospheric water generators—which take water vapor from the atmosphere and convert it to liquid water. This technology comes in three forms.
The first is fog nets, a very low-tech system that has been used for centuries in parts of Latin America where intense fog occurs on a regular basis, and people capture water with fabric nets. Fog harvesting is a variation on rainwater harvesting, but it is not ideal for most countries in Asia and the Pacific; for instance, rainwater contamination from volcanic sulfur emissions makes it impossible in places like Vanuatu.
Another option is condensation or dehumidification. Refrigeration technology converts water vapor to liquid, but it’s not energy-efficient. There’s a high risk of air pollutants contaminating the water, so dehumidifiers are generally not marketed as drinking water appliances.
The third type of atmospheric water generation is phase change, or conversion of water vapor to liquid form. For a long time, researchers have been trying to figure out a way to exploit the enormous amount of water waiting to be harvested in the atmosphere. The goal is to make highly efficient and affordable phase change devices to extract water vapor from the atmosphere and convert it to liquid.
If we want climate-proof drinking water, we need something that does not impact ground water or surface water, so we need to look at phase change devices. Even better, the device should run on renewable energy.
Traditional support from development organizations for access to energy programs generally emphasizes productive end-use of energy. Some have piloted energy storage systems, but few (if any) have tried to cross over to cover food and/or water.
In late 2016, ADB decided to bridge this gap by supporting a pilot project that addresses the energy-food-water nexus through atmospheric water generators.
We started looking at phase change powered by solar energy, by far the most abundant source of renewable energy. If we could mass-produce a reliable and affordable device, we have an infinitely scalable solution. And then, if we could tick all these boxes and deliver these devices like common household appliances, we could essentially “democratize” drinking water.
As part of the pilot, US company Zero Mass Water installed 4 of their SOURCE “hydropanels” on the roof of ADB headquarters in May 2017. The panels, which use a combination of solar photovoltaic and solar thermal energy units coupled with a proprietary nano-technology, selectively adsorb water vapor from the atmosphere and de-sorbs water in liquid form – the same as distilled water.
The nano-technology works like a molecular sieve, common in industrial dehydration processes like dehydration of natural gas so that it can be injected into pipelines. The hydropanels produce “double-distilled” water that is passed through a mineral block so that the product is similar in taste and composition to high-end bottled water.
These units are intended for residential and domestic use in areas where consumers rely on bottled water due to unreliable or non-existent water services. They’re also a good option for places with suspect water quality.
The hydropanels produce 2-5 liters of water per day and have been deployed in a variety of climates, including the Sonora desert in the US and Mexico. ADB is supporting deployment of 40 SOURCE units in the Philippines and another 20 units in Vanuatu on a pilot basis to further assess its technical and economic viability.
Although other phase change devices are commercially available, most rely on an external power source (some run on diesel generator sets) or are too large for practical use at the residential level and remote locations. The SOURCE hydropanels are self-powered, self-contained, readily transportable, and designed for household-level services. ADB encourages such technologies for use in developing countries, particularly remote communities lacking adequate access to clean water.
Atmospheric water generators also have good potential for responding to natural disasters, when conventional water supply systems are destroyed or out of commission for several days.
The potential for re-inventing drinking water supply chains is intriguing. With this family of devices, drinking water for poor consumers can be decoupled from traditional water treatment and piped water infrastructure.
Personal water ownership is therefore possible, similar to what we are doing with distributed renewable energy systems. We can also think of this as energy storage in a glass. Either way, it’s shaping as a potentially path-breaking means of tackling water security challenges in developing Asia.