Grooves spacing govern water retention during condensation

On smooth surfaces, condensing droplets grow, merge, and eventually slide away. Add narrow grooves, and the same water follows a hidden path: it drains through the surface itself. Using a high-throughput condensation setup, we show that groove spacing governs the transition between droplet shedding and capillary drainage. Below a critical spacing, grooves collect and channel all water before large drops can form, offering new routes for efficient dew harvesting and cooling.