Extreme Salt-Resisting Multistage Water Treatment

A multistage water treatment system that requires minimum energy and can be powered by low-grade energy sources, such as sunlight, is disclosed. The system may include multiple stages, where each stage comprises a hydrophobic membrane, a confined saline layer, and a condenser. Using a saline layer as the evaporator, as confined by a hydrophobic membrane, strong thermohaline convection is initiated to mitigate salt accumulation and enhance heat transfer. The multistage water treatment system is salt-resistant during continuous desalination of nearly saturated saline. Such a system enables water treatment by low-grade heat with water production exceeding the single-stage limit and ultrahigh salinity. This system is useful for water treatment, including seawater desalination, wastewater reclamation, residential water softening, and salt production from brine/seawater.