I have friends in the Philippines who saw this and so I did a few rough calcs to show why it might not work.. Ultimately you'd have to try one.. Remember this is for a warm/wet climate.. Sub Saharan Africa would be have MUCH less moisture to extract..:)
Condensing water takes energy.. Where does the energy come from? Well the energy comes from the warm moist air trying to heat the ground water. That means the ground temperature has to be below the dewpoint of the warm moist air. What is the dewpoint?.. Well that is highly dependent on the humidity of the air of course. Lets take a hot wet climate.. say Philippines at 95F and 50%RH. Well to condense the moisture means you will have to cool the air to 73F (100% RH). Thats the point at which you are JUST getting water. So now lets cool it further and get some more water say 70F.. . So how much water is this? Air at 95F and 50% contains 0.0176 lbs of H20 per pound of air. air at 70F and 100% contains 0.0156 lb/lb. So the water you get out is 0.002lb of h20/lb air. so to get 1 gallon of water (about 8.34lb/gallon) means you will have to cool 4170 lbs of air to 70F.. or about 59,000 cubic feet. Now do you think your ground water will stay at 70F if you start pumping this quantity of warm air down there?.. Air at 95F and 50% RH is 42.5Btu/lb. Air at 70F and 100% is 34 BTU/lb.. or 8.5 BTU/lb difference* 4170 = 35,500 BTU. Thats a lot of energy. for 1 gallon of water. Do you think the ground water won't warm up if you start putting that amount of energy down there? Thats hard to calculate but I my gut tells me this will become pretty ineffective, even in warm/wet climates. If you could get one for free to try out it would be worth it, but I'm skepitcal. Disclaimer.. I did the calcs very quickly, there maybe errors..