Passive fog harvesting by use of wire or fiber mesh is a common water collection method in Peru, Oman and other areas. This technique can secure sufficient supplies for drinking, cooking and other uses but is incapable of removing organic pollutants present in fog droplets. A remedy devised by researchers from ETH Zurich, Switzerland, and the Max Planck Institute for Polymer Research, Germany, not only collects water from fog but simultaneously purifies it.

A close-​mesh lattice of metal wire coated with a mixture of specially selected polymers and titanium dioxide forms the water collection system. The polymers ensure that droplets collect efficiently on the mesh and then quickly trickle down into a container before they can be blown off by the wind. The titanium dioxide functions as a chemical catalyst, breaking down organic pollutant molecules contained in the droplets to render them harmless.

The titanium dioxide is regenerated by ultraviolet light: half an hour of sunlight exposure is sufficient to reactivate the catalyst for another 24 hours. The catalyst also remains active for a lengthy period in the dark due to its photocatalytic memory properties, resulting in a water collection and purification system that requires little to no external energy input.

During laboratory and pilot plant tests conducted in Switzerland, the system was demonstrated to collect 8% of the water in artificially created fog and break down 94% of the organic compounds that had been added to it, including fine diesel droplets and the chemical bisphenol A.

In addition to supplying drinking water, the system detailed in Nature Sustainability is also envisioned for use in recovering water from steam at power plant cooling towers.