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27 April 2018

Fog Drip

Author/Compiled by
Eytan Gur (seecon international gmbh)
Dorothee Spuhler (seecon international gmbh)
Executive Summary

Fog harvesting provides a cheap complementary water source for arid and semiarid, rural regions. As the wind blows the fog through specially designed nets (fog collectors), tiny droplets of condensed water form on the mesh. They are collected in a gutter and transported to a storage site. The collected water does meet the WHO standards and can be used as drinking water. One large fog collector, with a 40 m2 collecting surface, can produce up to an average of 200 litres per day throughout the year. It costs around 1000 to 1500 USD each and can last 10 years.

Advantages
Passive collection system requiring no energy input to operate (FUREY 1998)
Cheap and easy to maintain and repair (FUREY 1998)
Water quality is generally goodin non-industrial areas, though pH can often be low (FUREY 1998)
Modular system that can grow in line with demand or available funds (FUREY 1998)
Quick and simple design and construction. Installation requires little time or skill (FUREY 1998)
Low capital investment and other costs compared to conventional sources of potable water inmountainous and arid areas (FUREY 1998)
Disadvantages
Technology requires very specific climatologic and topographic conditions. Yield is difficult to predict so a thorough pilot project is required in every case (FUREY 1998)
Yield is very sensitive to changes in climate conditionsand so a back-up supply is required (FUREY 1998)
Fog collection is unlikely to be of regional or national importance as a water supply. Emphasis is on the local level which requires full community participation (FUREY 1998)
If the collectors are not close to the point of use then the cost of the pipeline can make the system uneconomicand hydraulically difficult (FUREY 1998)
Vulnerability to vandalism (FUREY 1998)
Good access to the site is required for installation, maintenance and monitoring (FUREY 1998)
In Out

Precipitation, Freshwater, Drinking Water

Freshwater, Drinking Water

Factsheet Block Title
Introduction
Factsheet Block Body

(Adapted from MUNICH RE FOUNDATION n.y. and SCHEMENAUER & CERECEDA 1997)

The ever-growing need for freshwater in both developing and developed countries is indisputable and both increasing populations and the contamination (water pollution) of existing supplies will lead to constantly escalating demands. Water can be collected in almost every stage of the water cycle. The use of non-traditional water supplies such as the collection of fog must be considered as a complementary source and not as replacement. As clouds move over hills and mountains, the hilltops and ridge lines are enveloped in fogs.

 Fog produced by the flow of wind over terrain (right) and needles, with collected droplets from fog (left). Source: SCHEMENAUER (2008)

Fog produced by the flow of wind over terrain (right) and needles, with collected droplets from fog (left). Source: SCHEMENAUER (2008) 

Just as the leaves and needles of trees can collect some of the water in these fogs, large artificial collectors can produce a flow of potable water. Specially designed nets (fog collectors) are used to capture the moisture carried by the air. Tiny droplets of condensed water form on the mesh and are collected in a gutter and transported to a storage site. Other precipitation harvesting technologies for drinking water purposes are: rural rainwater harvesting, or urban rainwater harvesting).

Factsheet Block Title
Basic Design Principles
Factsheet Block Body

(Adapted from UNEP 1997 and SCHEMENAUER & CERECEDA 1997)

      Fog collectors on El Tofo Mountain, Chile. Water from the fog condenses on nets. Source: MUKERJI (n.y.)

Fog collectors on El Tofo Mountain, Chile. Water from the fog condenses on nets. Source: MUKERJI (n.y.) 

A fog collector is simply a frame that supports a section of mesh in a vertical plane. The large, operational fog collectors are typically made of two supporting posts, and cables on which the mesh is suspended. In addition, there is a network of guy wires to support the posts, a plastic trough to collect the water, and pipes to move water from the troughs to a reservoir or cistern. The large collectors are usually 12 m long and 6 m high. The mesh covers the upper 4 m of the collector. This gives a collecting surface of 48 m2 and typical water production rates of 150 to 750 litres per day depending on the site. Alternatively, the collectors may be more complex structures, made up of a series of such collection panels joined together. The number and size of the modules chosen will depend on local topography and the quality of the materials used in the panels. Multiple-unit systems have the advantage of a lower cost per unit of water produced, and the number of panels in use can be changed as climatic conditions and demand for water vary.

 


        A double layer of a polypropylene mesh is used to collect the fog droplets. Source: SCHEMENAUER & CERECEDA (1994)

A double layer of a polypropylene mesh is used to collect the fog droplets. Source: SCHEMENAUER & CERECEDA (1994)

The surface of fog collectors is usually made of fine-mesh nylon or polypropylene netting. Studies of various mesh densities in El Tofo (Chile) showed high efficiency at 35% coverage, mounted in double layers (UNEP 1997). This proportion of polypropylene-surface-to-opening extracts about 30% of the water from the fog passing through the nets (UNEP 1997). As water collects on the net, the droplets join to form larger drops that fall under the influence of gravity into a trough or gutter at the bottom of the panel, from which it is conveyed to a storage tank or cistern. The collector itself is completely passive, and the water is conveyed to the storage system by gravity. If site topography permits, the stored water can also be conveyed by gravity to the point of use. The storage and distribution system usually consists of a plastic channel or PVC pipe approximately 110 mm in diameter, which can be connected to a 20 nun to 25 nun diameter water hose for conveyance to the storage site/point of use (see also water distribution pipes) (UNEP 1997).

 


           Two large fog collectors and one large tank provide water for one or two families in Guatemala. Source: SCHEMENAUER (2008)

Two large fog collectors and one large tank provide water for one or two families in Guatemala. Source: SCHEMENAUER (2008) 

Storage facilities should be provided for at least 50% of the expected maximum daily volume of water consumed (UNEP 1997). However, because the fog phenomenon varies from day to day, it may be necessary to store additional water to meet demands on days when no fog water is collected. Chlorination of storage tanks may be necessary if the water is used for drinking or cooking purposes.

 


Factsheet Block Title
Cost Consideration
Factsheet Block Body

(Adapted from FOGQUEST n.y.)

Costs are variable depending on location, access and whether all labour costs are donated. The experience of FogQuest (www.fogquest.org) shows that small fog collectors for an evaluation cost 75 to 200 USD each to build. The large 40 m2 fog collectors cost about 1000 to 1500 USD each and can last 10 years. A village project producing about 2000 litres per day will cost about 15’000 USD.

Factsheet Block Title
Health Aspects
Factsheet Block Body

(Adapted from FOGQUEST n.y.)

Fog water chemistry has been studied and found to meet the WHO 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 (e.g. biosand filter, SODIS, chlorination; or in general HWTS).

Factsheet Block Title
At a Glance
Factsheet Block Body

Working Principle

As the fog moves through the nets tiny fog droplets accumulate on the mesh and join to form larger drops that fall under the influence of gravity into a trough or gutter at the bottom of the panel, from which it is conveyed to a storage tank or cistern.

Capacity/Adequacy

One large fog collector, with a 40 m2 collecting surface, will typically produce an average of 200 litres per day throughout the year. On some days no water is produced. On other days as much as 1000 litres will be generated (FOGQUEST n.y.).

Performance

Water harvested from fog meets the WHO drinking water standards (FOGQUEST n.y.).

Costs

The small fog collectors for an evaluation cost 75 to 200 USD each to build. A large 40 m2 fog collector costs about 1000 to 1500 USD each and can last 10 years. A village project producing about 2000 L a day will cost about 15’000 USD (FOGQUEST n.y.).

Self-help Compatibility

Expert knowledge needed for choosing the optimal location and material. The construction itself is simple.

O&M

Cheap and easy to maintain and repair (FUREY 1998).

Reliability

There are both day to day variations in fog-water production as well as seasonal variations, as is the case with rainfall (FOGQUEST n.y.).

Main strength

Low capital investment and other costs compared to conventional sources of potable water in mountainous and arid areas (FUREY 1998).

Main weakness

Yield varies from day to day as well as seasonal depending on the location (FOGQUEST n.y.).

Applicability

Fog collection is a resource that should be evaluated in areas where other traditional sources of water, for example, surface water, wells or rainwater collection, cannot meet the needs of the people and where a water pipeline or desalination plants are impractical or too costly. The application focus is located in arid and semiarid regions (SCHEMENAUER & CERECEDA 1997). Conditions for fog water harvesting are best where there are persistent winds from one direction to transport low-level cloud and advective fog (FUREY 1998).The map below indicates potential locations.

Black marked: places where fog harvesting studies have been conducted. Source: FUREY (1998)

Black marked: places where fog harvesting studies have been conducted. Source: FUREY (1998)


According to SCHEMENAUER (2008) there are two major applications for fog water collection in arid regions:

    Fog water used for growing Aloe Vera with a drip irrigation system at Faldo Verde, Chile. Source: SCHEMENAUER (2008)

Fog water used for growing Aloe Vera with a drip irrigation system at Faldo Verde, Chile. Source: SCHEMENAUER (2008)

  1. Fog collectors can provide water meeting WHO drinking water standards to rural communities and groups of homes; this water is inexpensive to produce and can be delivered to the homes by gravity flow.
  2. Fog collectors can provide water for reforestation of ridge lines and the upper parts of mountains where it is impractical to import water from conventional sources; the fog water can be delivered to drip irrigation systems by gravity flow and the resulting forests, if properly situated, can become self-sustaining by directly collecting fog water.

Also the potential use for agriculture has been studied, for example for a drip irrigation system as shown in the picture (SCHEMENAUER 2008).


Library References

Fog Research

This paper provides a scientific background on fog, including the definition of fog, the types of fog, and the relevance of fog in research.

EUGSTER, W. (2008) Fog Research, In: Die Erde . 139 ,1-2 . URL [Accessed: 13.07.2011]

F.A.Q.

FOGQUEST (n.y): F.A.Q., Toronto: FOGQUEST URL [Accessed: 18.06.2012]

Fog Collection

This is a general description about fog collection.

SCHEMENAUER, R. ; CERECEDA, P. ; (1997): Fog Collection, Norwich: Tiempo URL [Accessed: 13.07.2011]

Chapter 1.3 Fog harvesting

This document gives a brief technical overview over fog harvesting.

UNEP (1997): Chapter 1.3 Fog harvesting, UNEP (1998): Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean. Nairobi: . URL [Accessed: 20.07.2011]
Further Readings

Fog Research

This paper provides a scientific background on fog, including the definition of fog, the types of fog, and the relevance of fog in research.

EUGSTER, W. (2008) Fog Research, In: Die Erde . 139 ,1-2 . URL [Accessed: 13.07.2011]

Fog Collection

This is a general description about fog collection.

SCHEMENAUER, R. ; CERECEDA, P. ; (1997): Fog Collection, Norwich: Tiempo URL [Accessed: 13.07.2011]
Case Studies

Fog in El Tofo

This paper highlights critically the cultural (software) aspects of a fog harvesting project, which started in 1990 in El Tofo, Chile.

DALE, S. ; (2003): Fog in El Tofo, URL [Accessed: 20.07.2011]

Chapter 5.2 Fog harvesting in Chile

This document presents the technical aspects of afog harvesting project, which started in 1990 in El Tofo, Chile.

UNEP (1997): Chapter 5.2 Fog harvesting in Chile, UNEP (1998): Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean. Nairobi: . URL [Accessed: 20.07.2011]
Training Material

Chapter 1.3 Fog harvesting

This document gives a brief technical overview over fog harvesting.

UNEP (1997): Chapter 1.3 Fog harvesting, UNEP (1998): Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean. Nairobi: . URL [Accessed: 20.07.2011]

Alternative Versions to