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Comment by dale_glass | Hacker News Reader

Almost certainly nonsense. Similar things have been tried before, and as far as I know none worked. Reasons:

* If you have high humidity, you almost always have plentiful rain and water around.

* If you're in a desert, then there's extremely little for any device to work with.

* It takes absolutely enormous amounts of air to extract meaningful amounts of water even in favorable conditions. * It takes a huge amount of energy, too.

* Any such scheme isn't reliable in any case, and especially unreliable when things are dry and you really need the water. It works best precisely when you don't need it.

* You don't want to drink water from any kind of dehumidifier. It may have started clean, but won't stay that way.

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The scale is smaller but i have seen these machines https://www.waterfromair.co.za/ which do condense ambient humidity, filter and purify it and leave it in drinkable form. They look like water coolers without the giant bottle and function like a kind of dehumidifier with some additional steps.

Probably makes sense in a smaller scale “let’s replace our water coolers because water is scarce but we have enough energy” scenario like South Africa.

Currently in the bay area its 60-80% humidity. It also hasn't rained for weeks.

In the summer, certain parts of the Bay Area still has high humidity levels without rain for months on end.

> Currently in the bay area its 60-80% humidity. It also hasn't rained for weeks.

This brings back my summer Berlin memories. The temperatures are pushing 40, the air is so thick you feel like in Amazon rainforest. But no rain in sight.

You would need to extract 814,891,540 gallons of water to equal 1 inch of rainfall on just the city of San Francisco.

Some basic napkin math says at normal temp and humidity that is roughly 84 cubic miles of air you'd need to reduce to 0% humidity. Assuming the process isn't instant, you couldn't contain that volume of air in a structure humans know how to build. You'd also have to build massive air inlet pipes going 5 miles in each direction just to be able to circulate it into the machinery.

Edit: the comment I replied to was talking about areas with "humidity but not rain." I was just pointing out trying to replace rain is an insurmountable problem. You can do all sorts of things to optimize water usage, but that isn't the point. I picked San Francisco because it is a scale most people on HN can understand, but it is still tiny compared to farmland in the central valley.

Air circulates naturally, this idea won't work at all for other reasons but your calculations are:

1) for the whole city when these things are usually intended for households (and cities have many miles of pipes anyway.)

2) without mention of the rate of water extraction or energy use per liter which is usually what makes these obviously useless.

Yes and No. What percentage of the rain ended up back in the ocean? Suspect a very small percentage of rain actually ends up being used by humans.

You just need enough for the water that ends in taps or in the garden/farm.

I'm not saying this is preferred over desal, water recycling, or other water conservation/generation possibilities.

The region between alcatraz and pier 47 might be a bit higher.

Honestly I think it would be nice to have a magic drinking water creator, but wouldn't it be distilled water? (which isn't good for you, depleting minerals)

They do have uses is marketing. Vodka has a moisture harvested vodka "made with fog". It goes for 125 per bottle and is usually sold out as far as I can see.

That's a $100 premium which values the "fog" water at roughly $500 / gallon. So if you have a market willing to pay $500 / gallon extra for water harvested from the air this business might work. Not sure how many of those there are.

> It takes a huge amount of energy, too

This will often be more expensive than having a truck bring the water to you when running a dehumidifier especially when you are looking to get out enough for farming.

> * You don't want to drink water from any kind of dehumidifier. It may have started clean, but won't stay that way.

Why?

I have seen how gross dehumidifiers can be. But they are designed to dehumidify, not to provide drinking water. What is preventing one from purifying the water and keeping it that way?

I don't believe this will work but due to its complexity. And even if it will work, the life expectancy of some parts like solar panels is rather short. IMO projects like fog catchers [0] look much more promising.

[0] https://edition.cnn.com/2016/11/18/africa/fog-catchers-moroc...

It turns out there are a lot of places with humidity but little rainfall. Most of California being one but also places in the middle east. Believe it or not, there are high humidity deserts. There are several companies doing this not for farming but for drinking water. Like Zero Mass Water:

https://www.source.co/

Put another way, if there is enough humidity to work with then there are plants which have evolved to take in that humidity more efficiently than any apparatus. Imagine trying to design something that could compete with bamboo or certain bushes for extracting humidity from the air and either using it or transferring it to the surrounding microclimate.

There are numerous companies that make atmospheric water generators safe to drink that are in some cases solar powered and some that require higher input power. There are some units on Amazon that can do 8 gallons per day [1] and you can drink the water. That might be sufficient for a really small greenhouse using drip irrigation. You could store excess water in tanks. There are much bigger units but the cost goes up exponentially. These folks [2][3] make some bigger units. Here is a station that does 400,000 liters per day [4] Here is a more detailed video that describes the process. [5] There are also some hobbyists on youtube that are making DIY solar powered atmospheric water generators. I think there may come a time that we will need all available options. AWG's, Desalination Plants, Rain Capture at very least. Here is a 20k liter/day unit. [6]

[1] - https://www.amazon.com/NUBE-Generator-Ecological-Sustainable...

[2] - https://suntowater.com/

[3] - https://islandsky.com/products/

[4] - https://www.youtube.com/watch?v=yL3Ps86N2nM

[5] - https://www.youtube.com/watch?v=C1G2oC2cuTw

[6] - https://rainmakerww.com/technology-air-to-water/

I partly agree. But there's a long history of collecting moisture in the desert. For example: https://en.wikipedia.org/wiki/Air_well_(condenser)

Fog fences are used in some places to gather a small amount of water: https://en.wikipedia.org/wiki/Fog_collection?wprov=sfla1

Plentiful of rain need not equal plentiful of water around.

There are states in India for example that get 2000+ mm of rain every year and still have severe water shortages.

Is that because folks are pooping in the rivers? You’d think folks could just catch rainwater. Sounds like an infrastructure issue...

No, no large-scale pooping in rivers. Far more complicated than a single technological fix can handle.

Areas which get 2000+ mm of rainfall a year aren't always the ones with the most intensive agriculture. Water shortages are partly because of (a) the huge variation in the amount of rainfall from year-to-year in any area in India, and this variation has grown with climate change/warming (b) rivers down in the south of the country are not perennial but largely rain-fed during the monsoon. So "build more dams/infrastructure" doesn't make sense if there's not much rain to feed the rivers, (c) certain crops grown (sugarcane,paddy) just require tons of water, and are more likely to face issues due to variable rainfall compared to something like millet cultivation (d) rain is required not just for flow into rivers but for recharging groundwater, which is then used for agriculture. So, no rain = no groundwater and not just no rain = less flow in rivers.

Which highlights another problem with systems like these: Humans generally settle near sources of water already. The problems with water in poor countries is generally not one of water availability, but of water treatment.

Agreed

I'm not an expert by any means, but your comment reminds me of various nature documentaries in which desert species in certain locales would collect dew in the morning before it evaporates. Conceivably at least in such places it suggests that there is ample moisture in the air, and indeed if nature can get it out of the air then likely we could too. Conceivably an array of metal funnels leading to a bottle or tank (underground or otherwise protected from evaporation) could naturally harvest the moisture in such areas, even without a special hydrogel.

> huge amounts of energy

Condensation doesn't require energy. The energy mentioned in the article seems to be releasing the water from the hydrogel, but in my off-the-top-of-the-head metal funnel example a sufficiently steep big metal funnel can collect the water without any mechanical energy at all.

> Any such scheme isn't reliable in any case, and especially unreliable when things are dry and you really need the water. It works best precisely when you don't need it.

Water is stored easily enough, as long as you keep a surplus on hand for dry spells I don't see the problem?

EDIT: I am curious why my post is being downvoted. This doesn't seem particularly controversial.

Condensation requires energy input, or a considerable change in temperature.

Hot air can hold a lot of moisture, cold air can hold less. Water condenses on surfaces when the air cools down to the point that air would have to carry more water than it can at the new temperature.

Problem with that: it only works great in very humid areas. If you're in a desert, and have 10% humidity, you have to cool down your air by a lot for it to become too saturated and condensation to happen. Not enough cooling, and the moisture stays in the air.

> If you're in a desert, and have 10% humidity, you have to cool down your air by a lot for it to become too saturated and condensation to happen.

Deserts tend to have pretty wild temperature swings. They usually cool down at night. So much so that in most cases you can make ice. You can use the sky as a heat sink (effectively radiating heat into space).

https://www.fieldstudyoftheworld.com/persian-ice-house-how-m...

Thanks for the detailed information; that was genuinely informative, but I'm starting from the assumption that the required temperature swings must be present in at least some desert ecosystems as evidenced by the aforementioned documentaries. As the sibling noted, many deserts cool down quite a lot in the evenings.

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