Fog collection

A typical fog collector places a mesh panel across the path of fog-bearing wind. As air passes through, some suspended droplets strike and adhere to the mesh fibres. Droplets merge into larger drops, which run down the screen under gravity into a gutter and then through pipes to a tank or cistern. The system does not extract invisible water vapour from dry air: it intercepts liquid droplets already present in fog. It is generally passive and needs no pumping energy at the collector itself, although distribution or treatment elsewhere may require energy.

Fog collection is most promising where fog occurs frequently and wind carries it across an exposed collection area. Coastal hills and mountain ridges are among the settings where projects have been explored. Mesh material, droplet size, wind speed and direction, collector orientation, terrain, and season all influence how much water is captured. Yields therefore vary greatly from one location and period to another; a pilot collector and local meteorological measurements are useful before planning a larger supply.

Collected water can support irrigation and other local uses, and in some projects it supplements domestic water supplies. A complete scheme includes more than the mesh: gutters, conveyance pipes, storage, and arrangements for operating and maintaining the infrastructure are also needed. Projects work best when the scale and expected seasonal supply match community needs and local conditions. They are generally a supplementary, location-specific source rather than a universal replacement for conventional water systems.

The quality of harvested water cannot be assumed from its appearance or origin. Fog droplets may pick up airborne substances, while collection surfaces, pipes, tanks, animals, or handling can introduce contamination. Drinking-water use therefore calls for site-specific testing, suitable treatment where needed, and regular cleaning and inspection of the system. Strong winds can damage structures, and low-fog periods reduce production. Feasibility assessment, durable design, safe overflow and storage, and local maintenance capacity are important to a reliable project.