Good news.

From a brief look at the Airdrop link, some things come to mind. Thinking aloud, basically the method creates a situation where the air is conditioned such that air reaches the dew point and water condenses. This can be done by reducing the air temperature or increasing the air pressure. On days that we run our air conditioner, we often get two or three liters from the condensate pipe. Common practice is to plumb this "nuisance"  condensate to the drain. Due to increased pressure there is another nuisance condensate that needs to be drained from the shop air compressor tank. Unfortunately, air conditioners and shop compressors use up large amounts of power, especially if the primary purpose is to produce water.

It seems the Airdrop tries to use existing cooling from underground, but to reduce power consumption does not try to use pressure.

Problems that come to mind are,

for a decent sized vegetable garden, a famlly would need several tens of liters per day so the system would need to be large,

underground construction is expensive and gardening is fairly dynamic so these costs can be recurring,

copper is expensive,

underground system maintenance could be difficult.

Another thing comes to mind, with a large underground system, it might be advantageous to add living quarters to save on air conditioning and also have easier access to the Airdrop.

I like the subsurface watering feature. I find that once the water gets into the ground it tends to stay there if one has soil good for growing. I waste a lot of water and time trying to get water to roots. Soil amending and crop rotation may be a real issue with subsoil watering. Trees would probably be much less of a problem.

It would be nice to see the Airdrop scaled up to a household size and maybe integrated with other systems.

Just thinking (it's free, so I try to have seconds)
--
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/index.html
California, USA