Exploring freshwater generation in the Namib Desert: The potential of passive fog harvesting and solar stills

Abstract

Coastal nations such as Namibia are characterized by a distinctive desert environment that interfaces with the Atlantic Ocean. This unique geographic and climatic condition, influenced by the cold Benguela Current, generates a persistent fog belt along the coastal desert region. Our study evaluated the potential of passively harvesting this fog for the purpose of generating fresh water of desert irrigation. Fog nets (1 m²) facing south and west were established at the Henties Bay (coastal) site and at the Gobabeb (inland) site. The fog net direction significantly affected the quantity of water harvested with the south facing fog nets at Henties Bay recording an average of 6747 mL of water compared to 4855 mL per month for the west facing, whilst at the Gobabeb site, 5027 mL of water was recorded for the south compared to 2843 mL for the west, per month. The electrical conductivity of the fog water harvested at Henties Bay was however highly saline with electrical conductivity (EC) above 4000 µS/cm, with the highest EC being 40.93 mS/cm, whilst that from Gobabeb was moderately saline, with the highest EC of 2.69 mS/cm. Similarly, the fog water at the Henties Bay showed the highest concentrations of Cr (0.29 mg/L), Cd (0.056 mg/L), Cu (0.61 m mg/L) and Ni (1.89 mg/L), that were above the permissible levels of 0.1, 0.01, 0.2 and 0.2 mg/L, respectively. The use of solar still resulted in the generation of water that was of pristine quality with EC below 750 µS/cm. On average, the solar stills across both sites were able to generate between 33 and 166 mL of clean water per day. This research indicates that more fog water can be harvested at sites closer to the coast (Henties Bay) compared to sites further away from the coast (Gobabeb). However, the quality of the water harvested close to the coast will need to be desalinated, as the water is highly saline. Solar stills can be an effective, non-costly method of generating fresh pristine water from saline fog water, that can be effectively used for desert plants irrigation.