Extracting water from the atmosphere is catching on. But how viable is it, and what are the costs? Hema Vijay reports
E very school child knows that air contains moisture. But not many realize that the amount of moisture present in the earth's atmosphere at any point of time is about 12,900 cubic kilometres, which is 10 times more than the water content of all the rivers in the world put together!
With access to clean potable water becoming a major challenge across the world, it makes sense to cast the net wide to harvest potable water from all sources possible. Extracting water from the atmosphere is one such option many people are looking at now.
However, the idea of artificial atmospheric water extraction brings up some questions. How viable is the process? How pure is the water extracted? What about the carbon footprint of the process? And what about the direct environmental impact it might create?
Most modern atmospheric water extractors in the market work by sucking in air, cooling it below its dew point so that the water vapour in the air condenses to form water. Being an energy-driven process, this leaves its own carbon footprint; and in fact, desalination is certainly less expensive. But then, these machines give you potable water without drawing from a tangible water supply. As Chennai-based builder Satish Mehta, who has been using a water extractor in his home to cater for his drinking water requirements for the last three years, says, “It is freedom from the grid.”
Impact on climate
When we extract water from the atmosphere on a large scale, there is the risk of desertification. There are also questions concerning its impact on the monsoons, climate patterns, etc.
“If atmospheric water extraction is done on a very large scale, the desertification risk is certainly there; but I don't see this happening on a large scale because of the economics involved in energy-dependent water extractors,” says N. Ramjee, Scientist in Charge (Tamil Nadu), Centre for Environment Education, an autonomous body under the Ministry of Environment and Forests. Consider this: atmospheric water extractors that produce about 25 litres of water per day consume around 12 units of electricity per day. Taking into account the cost of the device, this roughly works out to a cost of around one to three rupees per litre, depending on the power tariff slab the consumer is in. There are water extracting systems that produce anything from 25 to 200 litres of water every day. “If photo voltaic cells are used to drive the process, it can turn out to be economically viable,” says alternative energy consultant L. Vasudev. So, it all boils down to volumes, and we need to stay well within the threshold volumes.
How pure is the water extracted from air? As of now, there is no Indian Standards Institution (ISI) certification for these machines. So firms like the Chennai-based Akash Ganga, one of the few indigenous firms manufacturing atmospheric water extractor units, take purity certification from labs like SGS India. The water is tested for acidity levels, colour, hardness, dissolved solids, calcium levels, magnesium, chlorides, sulphides, iron, silica and for biological agents like E Coli and coliform bacteria, to ensure that the water extracted conforms to drinking water specifications, as laid down by the Bureau of Indian Standards. “The extracted water can have no acid rain contamination because chemical particles like sulfates and nitrates in the air, which cause formation of acid rain are removed by an air filter before moisture is condensed,” says T.M. Shyam Sunder, director, Akash Ganga.
With these machines, the best water output is obtained at 50 to 70 per cent relative humidity and between 28-42 degrees Celsius. A lesser water output is produced even at 25 per cent relative humidity. Atmospheric water extractor units can be kept anywhere, but need access to fresh air, so they work best when placed by a window, or in the balcony or terrace.