Fully passive siphon-driven salt removal surpassing diffusion limits in solar distillation

Salt accumulation is a key bottleneck in solar- and waste-heat driven passive distillation systems, where evap- oration inevitably leads to salt buildup that compromises long-term performance. Here, the first evaporation- driven siphon architecture enabling fully passive and autonomous salt removal from a porous evaporator is introduced. The device operates in a fully passive manner, relying solely on evaporation-induced hy- draulic head differences. The system functions without external energy, active control, or moving parts. An analytical model, developed through the electric–hydraulic analogy, predicts both the transient evolution of evaporation-induced hydraulic head difference and the frequency of self-triggered rinsing cycles, and is validated experimentally under controlled conditions. A case study shows that the system generates hydraulic head differences exceeding 1.5 cm and triggers multiple rinsing events within hours. Parametric analysis reveals that geometry and hydraulic resistance of the porous evaporator strongly influence performance, and that a simple topological modification – introducing a localized high-resistance segment – further boosts hydraulic head buildup. Compared to state-of-the-art passive strategies limited by diffusion, the siphon- driven mechanism achieves over an order-of-magnitude faster salt removal, restoring seawater-level salinity within three hours. These results establish a new paradigm in solar distillation, providing a scalable strategy compatible with meter-scale evaporators and capable of drastically reducing maintenance requirements for robust salt management in evaporation-driven applications, e.g. desalination, particularly suited to off-grid and resource-limited environments