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Consider passive fog and dew collection (and their limits)

Fog nets and dew condensers need no electricity, but they only work at certain sites and give small amounts. Treat them as niche supplements.

How

1. Fog collection: a vertical mesh in a windy, foggy spot catches droplets that drain to a tank (Klemm et al. 2012). Operational projects typically average 3 to 10 L per m2 of mesh per day over a year, but yields vary greatly between sites.
2. Fog nets suit coastal or mountain sites with frequent fog and steady wind, where fresh water is scarce. They need near-saturated air (RSC 2020 review), so ordinary humid days are not enough.
3. Run a small test collector for a full season before building a large net.
4. Dew collection: a radiative condenser surface cools on clear nights and dew forms on it (Khalil et al. 2016). The theoretical ceiling is about 0.8 L per m2 per day, and recorded maximums are about 0.2 to 0.6 L per m2 per day.
5. Dew forms best on clear nights with light wind (yields fell sharply above about 3 to 4 m/s in one study) and humidity near saturation; one site saw no dew below about 79 to 81 percent RH (Khalil et al. 2016).
6. At those yields, dew suits garden or emergency top-ups, not household drinking water. Treat fog and dew water as untreated surface water before drinking (water-16).

Do these first

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Sources

1. Fog as a fresh-water resource: overview and perspectives (Klemm et al., Ambio, 2012). University of Pretoria repository, accessed 2026-11
2. A review: dew water collection from radiative passive collectors to recent developments of active collectors (Khalil et al., Sustainable Water Resources Management, 2016). Springer, accessed 2026-11
3. Energy performance and climate dependency of technologies for fresh water production from atmospheric water vapour (Environmental Science: Water Research and Technology, 2020). Royal Society of Chemistry, accessed 2026-11

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