Coastal fog or a marine layer are such common weather patterns in our area that over the years, many local people interested in innovative water sources have investigated collecting and using fog, especially during our typical 9-month dry season.
The fog catcher project just outside of Lima, Peru is a particularly inspiring story. Lima has a unique climate- rainfall is extremely low – less than 2 inches annually – but humidity can reach 98%.
And on the city outskirts, many residents do not have access to running water. South of the city, 32 fog catchers provide water to many of the district’s rural residents. These catchers are 12-by-18 feet high bamboo and metal frames draped with a thick mesh and capture between 50-100 gallons of water per day. Although not potable, the water is used for farming, cleaning, washing clothes and dishes, and even cooking.
A main researcher in fog collecting is Robert Shemenauer, and he has created the nonprofit fogquest.org which has initiated successful fog catchers in developing countries all over the globe. On the fogquest site there is a 100-page manual on how to build a "large fog collector" (LFC). Shemenauer’s research team has spent decades working out the bugs and doing the engineering. Pretty much all fog collectors around the world follow this manual, now. The fog cloth is basically a big sail, so tying it down properly is vital. This manual costs $35.
Some members of Sweetwater’s core group participated in a pilot study about fog catching in the Santa Barbara area in 2014. The study was hosted by the Mesa Harmony Garden. Some observations: Our coastal marine layer/fog is more stationary than the kind of wind driven fog that large sail-type fog collectors optimally need. Conditions for viable fog collecting are pretty specific, requiring high "liquid water content" and wind speed. It was determined that what is needed in our area is actually more akin to dew collection than fog collection.
What we have found that is successful in the Santa Barbara area are using rainwater harvesting tanks to collect dew from rooftops. During the dry season, tanks often partially re-fill because of dew on roofs in the morning. We have seen some significant capture using this method. It’s an added bonus aside from the rain collected during the winter months.