Fog harvesting, also called fog collection, captures moisture directly from fog using mesh nets, converting it into usable water without any electricity or machinery. It is an old idea getting renewed attention as climate change intensifies water shortages in vulnerable parts of the world.
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What Is Fog Harvesting?
Fog is made up of tiny suspended water droplets. Droplets are typically between 1 and 50 micrometres in diameter and form when humid air cools near ground level. In regions where fog is frequent but rainfall is limited, that moisture represents a significant untapped resource.
Fog harvesting works by placing large mesh nets in the path of wind-driven fog. As the fog moves through the mesh, droplets cling to the fibres, combine, grow heavier, and fall by gravity into a collection trough below. From there, the water is channelled into storage tanks for use in drinking, agriculture, or irrigation.
The concept draws inspiration from nature. The Namib Desert beetle collects moisture on its textured back; cacti spines channel fog droplets toward their roots; spider webs trap dew in fine droplet chains. Modern fog collector design increasingly borrows from these natural strategies.
How Does a Fog Harvesting System Work?
A standard fog collection system involves four main stages:
1. Capturing fog: Mesh nets made from polypropylene, nylon, or Raschel shade cloth. They are mounted vertically between two poles, positioned perpendicular to the prevailing wind. The size, density, and material of the mesh influence how effectively droplets are captured. The efficiency of collection depends on net material, hole size, filament diameter, and wind speed.
2. Forming droplets: As fog-laden wind passes through the mesh, tiny droplets accumulate on the fibres. They merge, grow larger, and eventually become heavy enough to run downward under gravity into a gutter at the base of the net.
3. Filtration: Collected water flows through a conveyance pipe to a storage tank. Before use, it passes through sand filters, cartridge filters, and UV treatment to remove particulates and microbial contamination.
4. Storage and distribution: Water is held in storage tanks and distributed to communities for drinking water, crop irrigation, or livestock use.
Under good fog conditions, a single square metre of mesh can produce between 2 and 10 litres of water per day. Large operational projects, like those in Eritrea and Cape Verde, have recorded daily yields of 4,000 to 12,000 litres across collector arrays.
Advantages and Disadvantages of Fog Harvesting
Is Fog Water Safe to Drink?
This is an important question, and the answer is nuanced. In rural or coastal settings with clean air, fog water generally meets WHO drinking water standards and has been found to be of good quality in projects across Morocco, Eritrea, and South Africa.
However, research has identified a range of potential contaminants in fog water collected in or near industrial and urban environments:
- Heavy metals: elevated concentrations of aluminium, iron, and in some cases lead and arsenic have been reported in collected fog water near industrial sites
- Acidic pH: sites near power plants or mining operations have recorded pH levels and mineral concentrations outside safe limits
- Biological contamination: some studies have found coliform bacteria and other pathogens in fog water, particularly where systems lack adequate maintenance
The composition of fog water reflects the air it forms in. This makes water quality monitoring essential for any fog harvesting system intended for human consumption, regardless of location.
Quality Control for Fog Harvesting Systems
A routine quality control programme is fundamental to keeping a fog harvesting system safe and functional. This should include:
- Regular inspection of mesh nets for structural damage, clogging, or loss of tension
- Cleaning pipes, gutters, and storage tanks to prevent algae growth, dust build-up, and microbial contamination
- Water quality testing, particularly for systems located near roads, agricultural land, or urban areas, where airborne pollutants can enter the fog. Testing should cover microbial parameters, pH, heavy metals, and nitrates
- First-flush diverters to redirect the initial, more contaminated water at the start of fog events
For any fog harvesting system intended to supply drinking water, laboratory-based water testing provides the most reliable safety assurance.
Case Study: The World’s Largest Fog Harvesting System
Morocco’s remote Ait Baamrane region sits well below the international water poverty line. Climate change-induced droughts push men to migrate for work, leaving women and children to make up the majority of village residents. Before fog harvesting arrived, women and children spent more than three hours a day travelling to distant, depleted wells.
The Dar Si Hmad project, a women-led NGO, designed and installed what is now the world’s largest fog water harvesting system. The results were transformative: reduced environmental degradation, fewer waterborne diseases, and hours returned to families each day. Vegetable growing became possible. As founder Jamila Bargach described it, the project restored both water and dignity to the community.
The Morocco example is one of dozens worldwide. Comparable projects operate in Yemen, Eritrea, Cape Verde, Bolivia, Chile, and parts of South Africa. Each adapted to local topography, fog frequency, and community needs.
The Future of Fog Harvesting
Research into fog collection technology is advancing rapidly. In 2023, engineers at UC Berkeley published work on a nanoengineered steel mesh coated with titanium dioxide nanoparticles. It can simultaneously collect fog water and break down organic pollutants using sunlight. This is a significant development for urban fog harvesting where air quality is a concern.
As climate change reduces the reliability of conventional freshwater sources, interest in fog harvesting as a complementary water supply strategy is growing. This isn’t exclusive to just arid regions, but in any area where fog is frequent and water security is a concern.
Water Testing With Southern Scientific
Fog harvesting is a low-cost, low-energy approach to fresh water collection that works with natural fog patterns. It supplies communities, supports agriculture, and reduces reliance on groundwater. Its simplicity is its strength, but as with any alternative water source, that simplicity does not remove the need for proper quality oversight.
Any fog harvesting system supplying water for human consumption should be supported by regular, laboratory-based water quality testing. If you are involved in a water supply scheme, Southern Scientific’s Standard Drinking Water Test and Comprehensive Drinking Water Test provide INAB-accredited analysis to confirm your water is safe.
