Coastal fog harvesting with mesh collectors where advection fog is reliable

Mechanism

Many arid coasts (driven by cold offshore currents) are dry on the ground but bathed in thick advection fog for months of the year. Fog harvesting hangs large vertical mesh panels perpendicular to the prevailing wind; fog droplets impact the mesh, coalesce, run down, and collect in a trough and reservoir, gravity-fed to villages. It needs no power, no membranes, no high-salinity intake, and no brine handling — making it intrinsically low-maintenance at the hardware level.

Where it fits

For communities on fog-rich coasts, this can be cheaper and simpler than any desalination. It applies only where the fog resource exists and is seasonal, so it typically supplements rather than fully replaces other supply. It pairs naturally with a professionalized maintenance model; its most famous failure is a textbook ownership/maintenance collapse.

Operating profile

• Dar Si Hmad's system: ~600 m² of nets, 7 reservoirs (~539 m³ storage), 6 solar panels, and 10+ km of piping deliver potable water to 400+ people across 5 villages via prepaid SMS-linked meters; later expanded with next-generation CloudFisher nets engineered to withstand higher winds and raise yield per panel.
• Yield is on the order of a few litres per square metre of mesh per day — more on the foggiest days, little to nothing outside the fog season — so reservoir sizing and a dry-season fallback are part of the design, not an afterthought.
• With no pressurised pumps, membranes or chemical dosing, the hardware is cheap to keep running; the binding costs are the civil works (masts, periodic mesh replacement, piping) and, above all, the institution that owns them.

Honest limits

• Geographically bounded. It works only where reliable advection fog exists — a relatively short list of cold-current coasts and high-altitude catchments — and is seasonal even there, so it cannot be a community's sole year-round source.
• Ownership decides survival, not hardware. The canonical fog project, El Tofo / Chungungo in Chile, collapsed socially rather than technically: once external support withdrew, no local entity owned upkeep, the mesh degraded, and the system fell out of use. This is precisely why fog harvesting must be coupled to a professionalised, funded maintenance model (sibling solution) instead of being handed over and left.
• Weather-dependent and uncertain year to year, so guaranteeing a fixed per-household allocation requires storage and a backup source.