Achille Knapen’s Air Well: From Ancient Greek Mounds to Dew Condensers

We are familiar with the billboards and water bottles that turn thin air into drinking water, yet the technology behind them is probably much older. Based on Friedrich Zibold’s discovery of thirteen large piles of stones in the Crimean peninsula in 1990, it was believed that the ancient Greeks already knew how to recover water from atmospheric water vapor plenty enough to supply water to the city of Theodosia.

Achille Knapen's Air Well

Zibold’s air well actually worked and it could produce 360 liters of water each day.

Each discovered conical pile was 10 meters tall and over 900 square meters wide. He also found fragments of pipes around the piles leading to the wells and fountains in the city. Zibold concluded these piles of stones were dew condensers that supplied water to the city. He also calculated that each condenser supplied more than 55,400 liters of water each day. Furthermore, Zibold constructed a similar condenser to verify his hypothesis by using large sea stones on top of a mountain near Theodosia. Luckily, Zibold’s condenser actually worked, and it produced up to 360 liters of water every day. However, His experiments with the condenser had to stop in 1915 due to the base developed leaks.

Achille Knapen's Air Well

Nevertheless, what Zibold identified as air wells were not condensers but actually ancient burial mounds. Recent studies have revealed that the yield of the condensers decreases dramatically as the mass of the structures increases because they cannot radiate away their heat quickly. Zibold’s condenser worked relatively well because of luck. That is, the shape of the stones allowed very minimal thermal contact creating thousands of small gaps through which air could pass. This allowed the stones to lose heat rapidly at night.


Zibold’s experiments continued to inspire different vapor-condensing mechanisms around the world.

Nevertheless, Zibold’s success with the condenser inspired different dew-catching mechanisms. Belgian inventor Achille Knapen’s large “air well” was one of them. It was built on top of a 600-foot high hill in Trans-en-Provence, France, between 1930 and 1931. Knapen’s air well or “le Puit Aerien” is 14 meters, and its walls are 3 meters thick to keep the inside temperature cool. A number of holes on the wall let in warm, moisture-laden air during the day, while at night, the water vapor in the air condenses against a huge concrete column built inside the structure and drips down to a collecting basin at the bottom. Unfortunately, Knapen’s air well had disappointingly low yield, generating no more than a few liters of water each day.


In recent years, several independent organizations in various countries have developed indigenous ways to collect drinking water from dew. For example, in the village of Chungungo, in Chile, fog collectors have been producing 15,000 liters of water a year for past several years. Another fog harvesting project in Lima, Peru, condenses fog in huge nets producing more than 2,200 liters of water per day.

Michel Royon
Achille Knapen's Air Well