[jerf]

In some sort of absolute sense, sure, water in the device is not water somewhere else. But with something like 326,000,000,000,000,000,000 gallons of water on Earth, it's well below the noise threshold. Even "dry desert air", if you work it out, has massive (heh, literally) amounts of water in it.

Plus the impact is even less than you think, because air that has been made dry is more able to pick up water, so you have to work even harder than you'd think to have any impact.

[ttul]

I used a moisture calculator to determine that 10% humidity desert air at 30 degrees celsius and 1013.25hPa air pressure contains 3.03g/m³ of water. At that rate, the air above a 100x100m football field (to altitude of 100m) contains 303kg of water, or 303L at 4 degrees celsius.

So you'd be "drying out" a very tiny cube of air to produce the water needed by an entire family per day even given desert conditions with one of these appliances.

In the first world, we use 100L/day for all our needs. That means if everyone in America lived in a desert, we might need 107,491,749,174,917.5 cubic meters of air to supply us with all our water. If that sounds like a lot of air, consider that Death Valley is 7.8e+9 square meters in area; thus, to supply ALL Americans with fresh water, you'd just need to suck Death Valley's air dry to an altitude of 10,000m or so.

[thaumasiotes]

> you'd just need to suck Death Valley's air dry to an altitude of 10,000m or so

It seems likely that, as the atmosphere becomes less dense with increasing altitude, so does atmospheric water. One cubic meter of air at sea level contains a lot more air than one cubic meter of air at 6,000m. Does your figure include that effect?

[ianai]

Anecdote but I routinely evaporate more water into air a mile higher than where I lived previously. It’s also much colder up here.

It all comes down to PV=nRT

If anything this would be much more like making sure the clouds drop their moisture where it’s sorely needed. I say this as someone who has many times seen the needed moisture fly by.

[tylerhou]

If you assume atmospheric water has the same density up to around 3000 feet, then you'd have to dry out 3 Death Valleys. Still pretty reasonable.

[portofcall]

At 3000 feet it’s about .9 atmospheres of pressure, but honestly humidity is incredibly variable. The lower pressure at 3k feet just places an upper bound on possible humidity, it doesn’t tell you what it is. My instinct is that you’re right, and we’re still talking about vast volumes of moist air. We could also “enrich” the air with solar powered evaporation of seawater and wastewater.

[jerf]

For the purposes of this discussion I'd say order-of-magnitude is close enough, and I doubt the number for Death Valley is off by more than two orders at most (taking into account the possibility that Death Valley is just too special to use the normal numbers on). It will take a lot of work to disrupt even a desert ecosystem by extracting water from the air, and we are precluded from even wanting to do that work by the immense energy expense it will involve.

[portofcall]

I agree, if we had the viable and affordable tech to do this, it would be low environmental impact. When you consider the impact of large scale ocean desalination, it would be a clear green choice.

[cwkoss]

Is that all personal water usage, or does that also include industry and agriculture?