Fog Net

What is it?

Passive water collection from fog using a stretched mesh — a way of obtaining water in regions where fog is frequent but rainfall is scarce.

What is it good for?

It is useful in coastal desert regions or mountain fog belts (e.g. the Atacama coast, Peru, Morocco's Anti-Atlas mountains, parts of South Africa) — places where the air is often foggy but rain rarely falls.

The physics behind it

Fog consists of tiny suspended water droplets (typically 1–40 microns in diameter) carried by the wind. When they drift toward a mesh with the right fiber thickness and gap size, the droplets cannot follow the air streamlines around the thin fibers, so they collide with the mesh (inertial impaction), coalesce there into larger drops, and run down under gravity into a collection gutter. Efficiency depends on the mesh geometry (the standard Raschel net with a shade coefficient of roughly 35–50% has proven empirically optimal), the wind speed, and the liquid water content of the fog.

History

It is a traditional practice among Andean and Chilean coastal communities, who observed for centuries that vegetation "combs" water out of the fog. The modern, engineered version was developed in Chile in the 1980s and 1990s (the Chungungo project) and then spread internationally from 1999 onward by the Canadian nonprofit FogQuest.

Simple version

A simple double layer of shade netting stretched over a basic frame, set perpendicular to the prevailing fog-bearing wind direction, with a collection gutter along the bottom.

Advanced version

An optimized Raschel mesh (roughly 35–50% shade coefficient, which empirically gives the best yield), standardized large panels ("Large Fog Collector", about 40 m²), with several panels installed in a row.

Industrial version

Networks of fog collectors feeding into small community water systems (e.g. a few coastal villages in Chile and Morocco), combined with storage and distribution infrastructure.

Building your own

A support frame (wooden or metal posts), the mesh stretched taut, oriented perpendicular to the prevailing fog-bearing wind direction (site-specific — it requires local wind observation), and a collection gutter along the bottom edge connected to a storage container.

Common mistakes

• Poor orientation relative to the prevailing wind direction
• A mesh with the wrong shade coefficient (too dense a mesh reduces airflow and deposition; too sparse a mesh reduces capture)
• Insufficient structural bracing — wind loads can be substantial
• No "first flush" filtering — dust and debris accumulated on the mesh can contaminate the first water collected

How to measure

Yield measurement (liters per m² of mesh per day), correlated with fog frequency and wind-speed logging, plus basic water-quality testing after collection.

Videos

(TODO)

Downloadable PDF

(TODO)