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/

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.

The model calculates the Gibbs free energy from removing water vapor, which takes property lookups at each condition. The data intensity comes into play because it's a full year averaged using hourly data, all across the globe.

To the other question: as the humidity goes to zero, the energy needs become extremely high. It also becomes very challenging for practical systems.

Temperature! See our figure from our paper and on wikipedia: https://en.wikipedia.org/wiki/Atmospheric_water_generator#/media/File:Least_work_AWH.png As seen, the energy needs is overlaid on a psychometric chart. The map itself is a yearly average, so it looks worse for regions that have dry seasons, even though AWH may be very easy in their wet seasons.. e.g. Look at Africa North and south of the Congo rainforest, or just South of the Amazon. Also, the map shows a strong influence of Hadley cells, with bands of low and high energy needs: https://en.wikipedia.org/wiki/Hadley_cell

It conveys the thermodynamic minimum possible, not what practical technologies can achieve. Available approaches are still emerging technologies, and may need an order of magnitude or more energy to work. For context, the minimum energy for seawater desalination is ~1 Wh /L.

Yup, AWH provides extremely high quality drinking water. And unlike other water treatment methods, there is no waste stream! It's especially suitable for remote arid regions. The amounts of water removed would be negligible compared to atmospheric flows, but for context, removing water should weaken storms. More info about the work here: https://engineering.purdue.edu/ME/News/2022/atmospheric-water-harvesting-can-we-get-water-out-of-thin-air

This lego map was created from figure 3a of our paper on Thermodynamic limits of Atmospheric Water Harvesting (link in the title). The original figure used hourly data and took weeks of run time on the Bell Cluster supercomputer to process the calculation.

Anyone can use our code on github to convert an image to the correct size, apply bins for colors, and visualize it before buying your legos: https://github.com/arao53/awh-limits/blob/main/lego_maps/warsinger_lego_maps.ipynb

More details about how to create your own Lego figures are on our post on Lego Education: https://www.reddit.com/r/LegoEducation/comments/zubefd/how_to_make_scientific_graphics_out_of_legos/