Frequently Asked Questions
The information below is drawn from both more than 20 years experience and from published papers and reports. More information is available in the FogQuest Fog Collection Manual (2005), which can be purchased from FogQuest. Detailed scientific and technical information is available, in the form of many published papers, to our members in the Members’ Section of this web site.
What is fog?
Fog is the same as a cloud except that it touches the ground, whereas a cloud has a base that is above the ground. When a cloud is moved by the wind and flows over and around a mountain, fog is present wherever the cloud touches the terrain. To a meteorologist, fog is present when the visibility is less than 1000 ft (about 300 m). What is important in the fog collection process is that fog is composed of tiny liquid water droplets from 1 to 40 micrometers (μm) in diameter. A typical droplet diameter is 10 μm.
How much water is in fog?
There is typically from 0.05 to 0.5 grams of liquid water in a cubic meter of fog.
Does fog collection work in humid air?
Our fog collection technology has many applications and can provide clean water in parts of the world where conventional sources are unavailable. But one must have fog and light winds, not merely high humidities or haze. Fog is composed of tiny liquid droplets. These are blown by the wind and impact on the fibers of a specially chosen mesh. Normally, visibilities should be less than 100 meters for successful fog collection.
Does it have to rain in order to collect fog?
It is not necessary that there be rain in order to collect fog, though the fog collectors are also efficient rainfall collectors. We sometimes work in desert areas where the annual rainfall averages less than 1 mm.
How does a fog collection project get started?
The projects usually start with an assessment of whether suitable conditions might be present at a location. If we feel this is the case, the community is willing to contribute to the project, there is funding for the project, and we have an effective local partner, we will do an evaluation with small fog collectors to see how much water is available and in what seasons. The suitable locations are usually hills with frequent cloud movement over their surfaces forming fog. This may well be at night. If the evaluation shows good water production, and the community is motivated to assist with the project and use the water, then large fog collectors can be built.
Can a fog collection project be done for a city?
We wouldn’t build fog collectors for a large city because the water demands are too high. Cities require huge amounts of water for infrastructure and industries.
Do I need electricity or generators to collect fog?
Fog collection is a passive process. The energy is supplied by the wind. In addition, the water moves by gravity from the fog collectors to the village, so no pumps or electricity are required to either generate or to move the water.
What are the costs for a fog collection project?
Costs are variable depending on location, access and whether all labor costs are donated. The small fog collectors for the evaluation cost $75 to $200 US each to build. The large 40 m2 fog collectors cost about $1000 to $1500 US each and can last 10 years. A village project producing about 2000 L a day will cost about $15,000 US.
How much water does a fog collector produce?
One large fog collector, with a 40 m2 collecting surface, will typically produce an average of 200 L per day throughout the year. On some days no water is produced. On other days as much as 1000 L will be generated. The variability depends on the site. Choosing an appropriate site is of utmost importance. There are both day to day variations in fog-water production as well as seasonal variations, as is the case with rainfall.
Is the fog water clean?
Fog water chemistry has been studied and found to meet World Health Organization drinking water standards. Because it is produced in remote areas few sources of potential contamination are present. Normally bacterial contamination would also not be an issue since it is very unlikely that there would be harmful bacteria in the fog. The mesh itself rapidly cleans itself from any dust that may have settled on it during a dry period. Once the water is produced by the fog collector the same precautions and considerations apply as for any other water source.
Is fog collection sustainable?
Fog collection can be a sustainable water supply for as long as the village and the local NGO maintain the system. This could be 10, 100 or 1000 years. The durability of a project will depend on the human component. The meteorological conditions that produce the fog are determined by large scale circulations in the atmosphere that change little over long periods of time.
What material is used in the fog collectors?
The meshes are made of polyethylene or polypropylene. They have been chosen to be very efficient at capturing the wind blown fog droplets. The material is produced by a few manufacturers. We buy it in Chile. It is produced in very large sizes for agricultural use. To date we do not know of a commercial source in Africa, North America or Asia. Other materials that might be suitable from a physics viewpoint usually have one or more drawbacks. The material must be efficient at droplet capture, be very cheap, be durable, be produced in large sizes (4 m or 8 m widths), produce clean water, and drain the collected water quickly.
Where can I buy the mesh for a fog collector?
FogQuest purchases the mesh that we use in Chile from a company called Marienberg. We do this because the price is reasonable, the company produces the mesh in 8 meter widths and very long lengths, and many of our applications are in Latin America. The contact information to order 35% shade coefficient Raschel mesh is:
Cia. de Mallas y Plasticos
Industrial y Comercial Marienberg Ltda.
Telephone: (56-2) 689 8031
We do not know of a suitable supplier in the United States or Canada. However, if you know of one that produces 35% shade coefficient, Raschel weave, u.v. protected polypropylene or polyethylene mesh, in large sizes, please let us know at firstname.lastname@example.org. Tildenet in the United Kingdom used to make the mesh but we do not believe it is available from them now. Other sources of the mesh have had some problems of quality and durability.
Note: we use the 35% Raschel mesh in a double layer. This is important to maximize the fog collection efficiency. The particular fiber width (about 1 mm) and the specific Raschel weave are both also important in order for the collection process to be efficient. It is not possible to put up any type of plastic mesh, metal screen, imaginative three-dimensional structure, or whatever, and expect to collect large amounts of fog water. You can see pictures of the double layer of mesh on our homepage. For copies of scientific publications discussing these issues, please write to email@example.com.
Will a fog collector collect rain?
Yes, a fog collector is a very good rain and drizzle collector. This is because wind-blown rain falls at an angle. A 40 m2 fog collector will collect much more rain or drizzle than falls on a 40 m2 area on the ground.
How should the fog collector array be designed?
The most experienced people in the layout of fog collectors are in FogQuest. We have gained our knowledge from both field tests and looking at the wide range of literature published over the years. This includes some older wind tunnel work looking at different arrays of fog collectors. Some of the general principles are covered in publications and in our manual. Because of the many issues involved, FogQuest always sends one of our experienced team to locate both the small Standard Fog Collectors (SFCs) and the Large Fog Collectors (LFCs) in new projects.
Some points to keep in mind:
- the best allocation of fog collectors is as single collectors with spacing between them of at least 5 meters
- two fog collectors built together, with three posts, also work well with little degradation in efficiency
- more than two collectors joined together should be avoided as it provides a major obstruction to the wind
- to ensure the fog is reattached to the surface, additional collectors should be placed behind upstream collectors at a distance of at least 10 times the height of the fog collectors, i.e. 60 m
- all topographical features, from microscale to macroscale influence the wind flow over the terrain; this, plus the influence of obstructions such as trees or buildings, must also be taken into account.
Does Coating the Surface of the Mesh with Special Chemicals Help the Fog Collection Process?
There is discussion on some Internet sites and in some publications about how putting hydrophilic (water loving) or hydrophobic (water hating) coatings on the material of a mesh might increase the water produced by a fog collector.
At the moment, there is no application in fog collection despite what some of the on-line sites have written about new materials for fog collection. We will explain this a bit below. FogQuest is a science-based NGO and Dr. Schemenauer has written papers looking at the fog collection process and the collection efficiency of fog collectors. To date these are the only actual field measurements of the collection efficiency and FogQuest uses this tested technology.
Fog collection is not a condensation process. It is an impaction process. Fog droplets exist in the liquid phase and have typical sizes from 1 to 40 um in diameter. The mean volume diameter is around 10 um in fogs where we work. The collection efficiency of a fiber for a fog droplet depends on the droplet diameter, fiber width and wind speed. The fluid dynamics determines the collection efficiency. The droplet knows nothing about the surface characteristics of the fiber until after it has impacted. The surface properties of the fiber can, however, influence drainage of water after the fog droplets are collected, though this is not a problem as we presently operate. Using our present mesh the collection efficiency for droplets arriving at the mesh surface is about 60%. It can never be 100% because the mesh has to be an open structure to allow the wind to move through. On the microscale, the collection efficiency of a droplet approaching an individual fiber in the mesh is 100% or close to it but the mesh coverage of 60% sets the limit to the overall collection efficiency. In practice, this produces a very good yield of fog water in well selected locations.
So, changing the surface characteristics of a mesh is not going to increase the fog water collected. It would also be difficult to have a practical mesh coating in real-world situations of very strong u.v. radiation, a wide range of temperatures, strong winds, rubbing of mesh surfaces by cables and other pieces of mesh. Coupled with this is the need for low cost, abilities to coat very large pieces of mesh in the production process, and durability in the field of ten years. Our big limitation in our water projects is not the need for a little bit more efficient mesh, it is the human component. When we work in remote villages in the developing world, projects succeed or fail depending on the motivation, contribution and long-term support of the villagers in the areas where we work.
Are there other uses for fog collection?
Reforestation is an example of how fog collection can benefit an ecosystem. If the higher hills in the area are tree covered and immersed frequently in fog, they will collect fog water and contribute to the aquifers. So, if the trees are lost through deforestation, the fog collectors can produce water for drip irrigation systems to rebuild the forests. The forests can then sustain themselves and contribute water to the ecosystem once again.
Can you answer my questions?
We try our best to be responsive and helpful. Please remember that anyone answering your request is an unpaid volunteer. As such, if you have a few clear questions that can be answered with a short reply, you will likely get your answers in a reasonable time. If you ask broad questions like, “ What are the social conditions in all the villages where there have been fog collection projects?” we will be unable to help you as the time required to write a proper response would be many hours.
I’m a journalist…
We recognize that journalists often have short deadlines but unfortunately we cannot stop everything and deal will multiple questions, especially those that require long responses. Please understand that we receive several requests from journalists each week. Also, it is not part of FogQuest’s mandate to assist for-profit businesses or freelance journalists prepare a piece to sell. However, we try to be as helpful as we can. So, if you could have questions that require short responses or a short telephone conversation it would be appreciated. Similarly, requests for “high resolution copies of all the photos in the brochure and poster” are unrealistic. We appreciate your interest in FogQuest and fog collection and will try to help within the resources we have available.
Can I get a copy of the photo…?
We appreciate your interest in fog collection and we do have a large selection of images available from our projects as well as the projects of the 1980s and 1990s but we do not make images freely available to for-profit businesses. First, because it takes a lot of time on our part to locate them and to send them. And second, because FogQuest makes a small but important amount of income through photo rights for the use of our photos. These fees are regularly paid by print and web-site publishers and the fees are used to support our village water projects.
Please visit the image gallery to see our available selections.
To request a photo or to inquire about fees for reproduction rights, please write to firstname.lastname@example.org.
How can I help?
– becoming a member; the modest annual fee helps keep FogQuest alive
– making a cash donation or donate air miles
– making a presentation about FogQuest to your school or organization
– raising funds for FogQuest through an activity or event
– committing time to help FogQuest as a volunteer