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oo, fermi estimate time!

Typical 50% RH at ground level is ~7g/kg air, air is roughly 1kg/m^3, so between the surface and the planetary boundary layer (let's say 1km) is about 7L of water per m^2 of surface. Moving along at ~3m/s means 21L/s passes by each meter of fence line.

PBL probably mixes after about 50km, so it takes ~5 hours to normalize after you pull out water at ~5 knot wind speed. If you want to not make a dent, means you can pull less than 1L per m^2 per hour, or about 8m^3 pear, which is about 8x the yearly requirement for farmland.

So, you can irrigate a farm and your neighbors would mostly be fine.

(math not checked)

There are commercially available systems that do that now, one that seems popular in my area is https://www.aquaria.world/ .

As to your question, would it be a problem if everyone did it -- it depends obviously on your definition of "problem", but consider that most people doing this have no way to dispose of the water they take from the air except by putting it back in the air. It might increase regional power consumption, and smooth out nightly shifts in atmospheric humidity, but unless there is a new river running to the sea, the average atmospheric humidity will remain the same.

In humid regions, there is no practical limit that would cause any noticeable effects on the humidity of outdoor air. There is just so much water in the air that even if you were running dehumidifiers across all available land area, the air is still going to feel humid.

It would probably depend on how you use the water. Watering plants (including via gray water systems) would mean a lot of the water would evaporate or transpirate. Flushing it down the drain means it exits the system.

> I've thought for a while that it would be interesting to have micro dehumidifiers on my roof that supplement my water supply from humidity.

Hi! This is friendly neighborhood energy conservation law speaking!

You can't just get moisture out of the atmosphere without investing energy. This device works backwards, it exploits the difference in humidity between the indoors and the outdoors. The source of this difference is ultimately the stored energy in food. Humans burn the food and release water vapor as a result, raising humidity inside the building.

For non-potable use, probably. Potable use might require some more treatment checks on it. It's one thing to use it for flushing the toilet... showering might be ok. Not sure about washing dishes. Washing clothes, maybe.

And for the "the amount of times I change out 2 gallons of water from the dehumidifier in the basement in the summer"... there's a lot of moisture out there.

This is constrained by season. In the winter, its much easier to get to 0% humidity than it is in the summer.

https://tropic.ssec.wisc.edu/real-time/mtpw2/product.php?col... for the total precipitable water over North America. Through the midwest, it's in the 40-50mm range.

Consider XKCD's giant raindrop - https://what-if.xkcd.com/12/

> We’ll imagine our storm measures 100 kilometers on each side and has a high TPW content of 6 centimeters. This means the water in our rainstorm would have a volume of: 100km x 100km x 6cm = 0.6km^3

> That water would weigh 600 million tons (which happens to be about the current weight of our species). Normally, a portion of this water would fall, scattered, as rain—at most, 6 centimeters of it.

Change that to 4cm for current conditions... but that's a lot of water.

https://en.wikipedia.org/wiki/Humidity#Relationship_between_...

That has a table of how much water at different humidity and temperature combinations. It's currently about 20 °C and that gives us 15.6 g/m^3.

... but there's an awful lot of air around.

This can also be complicated if you have trees or other vegetation around. The humidity at my parents place (fairly deep in the woods in farmland) is always much higher than it is if you go to the road (or in town).

https://extension.osu.edu/about/resources/corn-sweat-and-hum...

> Some research conducted by USDA Agricultural Research Service suggests that corn can contribute between 3,500 and 5,000 gallons of water per acre to the atmosphere over the course of one to two days. A typical pool contains 18,000 - 20,000 gallons.

...

So, it's complicated. Maybe, a little bit, depends on where you are.

Depends on your region, house, and preferences:

https://midwesthvacpro.com/what-should-indoor-humidity-be-a-...

Bad by what metric?

The condensate (water vapor that gets condensed out of the air in the process of generating the electricity) has to go somewhere; if it's not properly handled, yes, I would expect mold.

Mold isn't really your main concern tbh. Instead it would be Legionnaires' Disease.

https://en.wikipedia.org/wiki/Legionnaires%27_disease

Some heat pumps have built-in UV-C sanitization to prevent mold.

You can install an aftermarket UVC light to sanitize to prevent mold in heat pumps, humidifiers, etc