Water potential not lost in coastal fog

With the help of area researchers, the district installed experimental fog-catchers over the summer at three district sites — Milagra Ridge, Christen Hill off Skyline Boulevard, and Royce Canyon near Fassler Avenue — and are monitoring their production. 

The fog-catching devices are simple: a 1-meter square of polyethylene mesh stretched over a frame and installed facing into the prevailing wind. When the fog blows in, the mesh collects droplets of water like a giant spider web. The drops fall into a collecting trough below and flow through a gauge that measures the amount of water. 

On a recent Saturday at Milagra Ridge, professor Daniel Fernandez from California State University, Monterey Bay, worked with some of his students to install two new nets. Fernandez supplied and installed the district’s fog-catchers and is studying their performance. The new nets held different kinds of meshes to test any difference in their water-catching abilities. 

His students are monitoring the three Pacifica sites, and they’re particularly excited about the Milagra Ridge results. Over the past two months, they recorded 300 liters of water — nearly 80 gallons — from that collector. “That’s better than what I’ve seen anywhere around Monterey Bay,” Fernandez said. The Christen Hill site is also promising. 

A good site needs enough elevation to be in the middle of the fogbank, and wind to push the fog through the mesh. Both features are abundant in Pacifica. 

How likely is it that fog would be a significant water source for the city? There are fog-catching installations in South America that produce over 500 gallons a day, supplying villages with a significant water supply. But those installations involve arrays of large collectors, and they service very small communities that have few other water options.

“To supply a city the size of Pacifica? No, you’re not going to get that from fog,” said Fernandez.

Adrianne Carr, manager of the NCCWD, agrees that fog would not likely become a source of potable water for the city. “It would be hard to put it into our regular water supply. There are lots of regulations around that.” What is more feasible is that fog could become a way to stretch those water supplies by providing nonpotable water for uses such as gardening.

There is customer interest in backyard fog collectors, said Carr. If the district’s

experiments show that fog collecting is worthwhile in Pacifica, she said, “maybe

we could do a rebate program like with our rain barrels.”

One benefit of fog in landscaping is that it’s most common during the dry summer season. Coastal vegetation naturally takes advantage of this: Fog drip is known to be an important water source for plants such as redwoods and manzanita during the long rainless months. 

Samantha Hauser, who first proposed the idea of catching fog to the district, has a vision beyond the practical applications.

“I’d love for us to do a sculptural version of a fog-catcher,” she said, as a public art project expressing the essence of the city of fog.