Fog fence

A fog fence is an apparatus for collecting liquid water from fog, consisting of a fine mesh deployed in a manner similar to a fence. 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.

Principle
Fog contains about 0.05 kilo grams of water per cubic meter, 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 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.

Limitations
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.