Water harvesting from soils by light-to-heat induced evaporation and capillary water migration

Freshwater scarcity is one of the critical challenges for global sustainable development. Several novel water resources, such as passive seawater solar desalination and atmospheric water harvesting, have made some progress in recent years. However, no investigation has referred to harvesting water from shallow subsurface soils, which are potential huge water reservoirs. Here, we introduce a method of light-driven water harvesting from soils, which can provide cheap freshwater of very high quality in impoverished, arid, and decentralized areas. Concentrated solar energy is used to heat the soils to evaporate the soil moisture. Then vapors flow to the condenser through tubes and condense as freshwater. Sustainable water harvesting is realized by water migration due to the capillary pumping effect within soils. In the laboratory conditions, an experimental setup was designed and its water-harvesting ability from soils was investigated. The maximum water mass harvesting rate was 99.8 g h(-1). Considering the dimensions of the samples, the maximum water harvesting rate per cubic meter of the samples could be recalculated to be about 12.0 kg h(-1) m(-3). In about 12 h, the total harvesting water could be as high as about 900 ml. The energy efficiency of our method was also estimated to be about 2.6-21.6%, depending on the heating powers and soil water contents. Then the water harvesting rate of one sun energy flux (1 kW m(-2)) was estimated to be approximately 360 g h(-1) with a 1 m(2) solar concentrator. Furthermore, the testing results of the water quality indicate that the collected water was high-quality drinking water. Our proposal provides a potential onsite and sustainable freshwater supply solution to deal with the water scarcity problem in impoverished, arid, and coastal regions after natural disasters.