Fog fence

A fog fence or fog collector is an apparatus for collecting liquid water from fog, using a fine mesh or array of parallel wires. Proposed geometries include linear, similar to a fence and cylindrical. It has the advantage of being passive, requiring no external energy source to perform its collection. This makes it attractive for deployment in less developed areas. An ideal location for fog fences is high arid areas near cold offshore currents, where fog is common. Fog fences are an ancient device with origins stretching back as far as the Inca Empire.

A related, but quite distinct, technique of obtaining atmospheric moisture is the air well.

Fog contains typically from 0.05 to 0.5 grams of water per cubic metre, with droplets from 1 to 40 micrometres in diameter. It settles slowly and is carried by wind. Therefore, an efficient fog fence must be placed facing the prevailing winds, and must be a fine mesh, as wind would flow around a solid wall and take the fog with it.

The water droplets in the fog deposit on the mesh. A second mesh rubbing against the first causes the droplets to coalesce and run to the bottom of the meshes, where the water may be collected and led away.

Fog fences are limited by the local climate and topography. Their yield is affected by local weather and global weather fluctuations (such as El Niño). Windborne dust can cause contamination of the collected water. The moisture collected can promote growth of mold and other possibly toxic microorganisms on the mesh. Birds and insects can also be sources of contamination.

...
Wikipedia