Drink the air!
From spider webs to sophisticated machines
The first effective initiatives to harvest water from the air were very simple—little more than panels placed in the fog. The condensation that formed on the surfaces ran down into a gutter system and into a tank for storage. This practice drew inspiration from the way spider webs are covered in dew drops in the morning. It is an inexpensive, passive system requiring no energy, but effective only when the air is saturated with water vapour. Systems using solar radiation have demonstrated their effectiveness in drier settings. These work somewhat like windows, with condensation forming between the panes under the sun’s intense rays. Active water harvesting systems are more well known. They are very effective but energy-intensive, which makes them difficult to use as water supply systems. The most common kind of water harvesting device is an air dehumidifier.
What about your dehumidifier?
The water collected by a dehumidifier is demineralized and therefore has no nutritional value; it should not be consumed and is not recommended for watering plants, as they need the minerals usually found in water. Furthermore, there is a risk of contamination, which may be caused by one of the following factors:
- The water could contain traces of metal (usually lead) from the welding on parts in contact with the water; this risk is also present in buildings with old plumbing.
- The stagnation of the water in the reservoir favours the development of pathogenic organisms.
However, the water collected by your humidifier would be ideal to use in your steam iron.
A solution for the future
Today’s moisture harvesting methods have evolved a great deal. In 2009, German researchers developed a solar-powered active harvesting system. It seems this system is equally effective in the desert! Yes, even in the driest part of the Sahara, the air contains water—especially at night.In fact, the relative humidity there varies between 4 and 20% in summer—by comparison, Montréal’s relative humidity during the same period is generally between 55 and 60%.
This is how it works: a saline solution absorbs and holds the moisture. In the solar-powered boiler, the water is separated from the saline solution by evaporation. The water is then collected in a tank and the saline solution is reused to harvest more water. Like many environmental issues, there is no single solution but rather a set of adapted solutions that, together, can have a major positive impact. This new moisture harvesting technology may be among the strategies that solve water supply problems in certain parts of the world in the future. However, although this new type of system can produce potable water, the available information seems to show that the water is distilled—that is, demineralized like humidifier water—which raises the question: would you drink the water from your dehumidifier? To be continued...