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WaterScienceProf OP t1_j25vg4q wrote

Reply to comment by something-quirky- in Lego world map of energy to harvest water from the atmosphere [OC] https://doi.org/10.1039/d2ee01071b by WaterScienceProf

The atmosphere holds about 12,000 km^2 of water, and the average human needs 8 cups of water per day (the main application of AWH). Thus, it we provided all human drinking water with AWH, it would be about 0.0001%/day.

On a sustainability note, right now the use of river water for drinking can be ecologically damaging, as many water resources are fully exhausted. e.g. the Colorado River and Rio Grande in parts entirely dry up. AWH is a more sustainable source, as the sun provides plenty of continuous evaporation to add more water vapor.

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something-quirky- t1_j264xk1 wrote

I think you’re forgetting is that the atmospheric harvesting wouldn’t be evenly distributed across the globe. As your map points out, there would be spots that would be better then other. So you’d expect that the harvesting plants would be not be evenly distributed. So while you may only be extracting some fraction of a percent from the entire globe, you’d be extracting a much larger percentage in the context of the local area. It’s like saying “its okay if i drain this lake because it only takes up .00001% of global fresh water” meanwhile you’ve used up 10% of the LOCAL freshwater. You’re also mischaracterizing the problem. Sure, humans only need 8 cups of water to drink… but you also need to use the toilet, and take a shower, and wash your clothes, and wash your dishes, and cook etc. And you can’t just pump in dirty water for everything that isn’t for drinking. It’s just passing the buck is what it is, and I’d be willing to bet that the resulting weather patterns from this practice would be just as devastating as draining the rivers and streams.

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WaterScienceProf OP t1_j2782pb wrote

Water in the atmosphere is a near infinite resource. It stays up on average only 8-10 days, being continuously regenerated by the sun. I don’t mean to be dismissive, but the amount of water in the atmosphere dwarfs currently used freshwater sources by orders of magnitude. And unlike other methods, it doesn’t produce wastestreams, which can be ecologically damaging especially if said wastewater is salty and far from an ocean.

When we pump in dirty water for things besides drinking, it’s called greywater reuse, and is actually far more widespread than AWH.

The real concerns for AWH are around its energy intensity, which is many times that of conventional sources- as a result it’s likely not economically viable for use beyond ultra pure water. And if it’s not powered by renewables it may not be sustainable. And renewable power is still resource intensive to create. You are right to criticize it, but you focused on the wrong issue!

Sources: https://hess.copernicus.org/articles/21/779/2017/hess-21-779-2017.html https://greywateraction.org/greywater-reuse/

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