Watery delusions

This is touching on something I covered in a previous post, however, there has been a proliferation of such devices recently, so I think it needs revisiting.

prevot-water-uc-berkeley

Figure 1: Concurrent with the global water crisis, there’s been a proliferation in water from air devices recently, with even university’s (this one from Berkeley) getting in on the act

We are in the grip of a global water crisis effecting millions of people around the world, such as California’s central valley, farmers in rural India or the city of Cape town. Primarily these are caused by the misuse of finite water resources, although climate change and shifting weather patterns are starting to make things much worse.

liquid-planet-940x830

Figure 2: Water scarcity is a growing problem, including in some developed countries

It is perhaps inevitable than in such times people will seek miracle solutions. One of those is the concept of generating water from air. And like I said, there has been an explosion in the number of such projects over the last few years, often in the very countries undergoing water stress. There’s been an X-prize for them and one such device even popped up on Dragon’s den a few years ago. My dad was even approached recently by a door to door salesman trying to sell such a device.

They claim water from air devices are “more environmentally friendly. In reality, they are about the most expensive and unenvironmentally friendly way to source water. And for these reasons many of these ventures eventually fail, sometimes leaving those who invested in them out of pocket, such as the Fontus and Waterseer devices I covered in a prior post a few years ago.

So what is the problem with sourcing water from air? Well, anything that involves heating, cooling or condensing of water is always going to be energy intensive. To get water from air it has to be first cooled to its dew point and then condensed from a gas to a liquid. Cooling 1L of water down 1°C requires 4,200 Joules of energy. So cooling it 10°C requires 42,000 J, which is about equivalent to the energy contained in a typical mobile phone battery (mine holds about 0.012 kWh’s which would be about 44,000J). To condense from a gas into a liquid (creating bonds that hold it in liquid form) requires far more energy, for water an extra 2 million Joules per litre (or 0.611 kWh’s per litre, enough to charge a phone 50 times) is required.

Atmospheric_Water_Generator_diagram.svg

Figure 3: How a dehumidifier water from air device works

Performance can be improved by using a heat pump (i.e. a refrigeration unit which “pumps” more heat than is required to run the heat pump) or a desiccant (which essentially acting as a catalyst to speed up the process). But these processes have their limits (e.g. a heat pump can only operate so long as there is a set of hot and cold reservoirs to pump heat between, if one or both is depleted it stops working). Hence, industrial dehumidifiers (as essentially what we are talking about is a glorified dehumidifier) extract water from air at a rate of between 1.5-3.7 L/kWh. By way of comparison, water treatment in the UK has an energy cost of about 1500 L/kWh, making it hundreds of times more energy efficient (and thus significantly cheaper). Groundwater extraction has an energy cost of about 1000 L/kWh, while desalination of seawater by Reverse Osmosis works out at about 250 L/kWh.

watr_from_air_l_kwh

Figure 4: The water extraction rate per unit energy by different methods, references given in previous paragraph

Furthermore, the quantity of water in air is tiny. In my office right now, its 20°C with a relative humidity of 40%, which means there’s just 6.92 grams of water per cubic metre (about ½ a tablespoon!). Even at 100% humidity we get merely 17 grams of water, about 1.2 tablespoons! So a dehumidifier is going to have to suck in vast quantities of air just to extract a few litres of water. And, if operated indoors, it will gradually dry out the air in your house (humidity should be kept at 30-50% indoors in order to avoid various health issues and to avoid damaging the building fabric).

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Figure 5: Even at fairly high levels of humidity, the amount of water in the air is tiny

In addition, the manufacturers of dehumidifiers generally recommend that you don’t drink the water, as it will contain anything else that’s been floating around in the air (dust, bacteria, whatever the dog’s been chewing). You can of course filter it (as some of these devices do), but that comes with a further energy cost and a maintenance cost. Also water from air will taste awful (this came up in the aforementioned Dragon’s den video) as its been completely de-mineralised (in truth it has no taste, but your body doesn’t know how to process that so it sometimes proscribes a nasty taste to it instead).

There has also been a proliferation of water quality scams doing the rounds, where a door to door salesperson (such as the one who visited my dad) will claim your tap water is dangerous and try to sell an expensive filtration system (instead of one of these water from air devices). For example the “water quality test” with electrodes in the aforementioned dragon’s den video, is a known scam. Canada’s CBC news has a report on these scams from 2017.

PT-20151606-Water-Testing-Scam-Header

Figure 6: This so-called “water quality test” is a scam with no scientific basis what so ever, similar ones using chemicals to produce the same result are also a scam

Municipal water supplies are subject to regular testing (by law), the results of which are often available online. Unless you have been told otherwise by your water supplier, it should be fine (they are legally required to report any issues). In any event, it makes more sense that they fix the problem than homeowners buying expensive equipment (for the record, my dad, guessing this was BS, had a word with his local council who sent him the details of their regular water tests, and yes its fine, nothing wrong with it).

There are some niche roles a water from air device can perform. Military applications and disaster relief for example. Or alternatively, in situations where you have high humidity and low rainfall. That said, there are other established low tech methods that can extract water, which don’t require a dehumidifier. So in almost all cases, its going to be significantly more environmentally friendly to source water by more conventional means.

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Figure 7: So called fog catcher nets are an effective low tech way of collecting water…and they don’t need a expensive dehumidifier!

For this is the cold hard truth. The solutions to the global water crisis are the same as experts have been pointing to for decades. Better water conservation (no more manicured green lawns or golf courses in a drought stricken country, promoting drip irrigation of crops, collection and reuse of grey water), banning wasteful practices (such as growing water intensive cash crops in a water scarce area), treatment of sewage and industrial waste, sinking more wells, build more reservoirs, etc. And if all else fails, consider investing in desalination, as Israel has demonstrated.

But of course, the whole reason we have a water crisis is because these are the answers that nobody wants to hear. It would mean taking on powerful lobby groups and voting blocks (notably farmers), as well as wealthy vested interests. It would mean investing considerable sums of money on large infrastructure projects. So instead, it’s all too easy to cling to some fantasy solution and kick the can down the road.

truth-vs-lies

Figure 8: Unfortunately people will often place comforting lies above cold hard truths, its the basis behind lotteries, politics and major religions

Which is what worries me about these water from air devices. While yes some of those promoting them are charlatans preying on people’s ignorance, others are well meaning enough and genuinely trying to make a difference. However, all they are likely to succeed in doing is making a global water crisis worse, by giving the powers that be the excuse to do nothing.

And I fear water from air devices are only the start. We see all sorts of purported miracle cures for Covid-19 doing the rounds, which even politicians are sometimes buying into, none of which are likely to work (its likely Trump btw has a financial stake in the company behind some of these). No doubt when the oil starts to run out, rather than investing in sensible solutions (renewables, energy conservation, etc.) instead we might see a sudden renewed interest in water powered cars and cold fusion.

About daryan12

Engineer, expertise: Energy, Sustainablity, Computer Aided Engineering, Renewables technology
This entry was posted in aviation, clean energy, climate change, economics, efficiency, energy, environment, fossil fuels, future, Global warming denial, history, news, peak oil, politics, power, renewables, sustainability, sustainable, technology, water scams and tagged , , , , , , , , , , , , , , , , , , , , , , , , . Bookmark the permalink.

3 Responses to Watery delusions

  1. neilrieck says:

    In 2020 there seems to be an uptick of magical thinking (both “religious” as well as “snake oil”)

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