We fabricate a bioinspired spindle-knotted fiber (BSF) via an improved method of Rayleigh instability break-up droplets. The BSF is composed of multi-level spindle-knots that can generate continuous gradients of surface energy and different Laplace pressures. We investigate the water collecting ability of BSF under humid environments and observe how the spindle-knots collect water from the environmental humidity by means of cooperative driving forces resulting from individual spindle-knots. We reveal that the multi-level spindle-knots of BSF may play a role in water collection compared with uniform fibers without any spindle-knots. We demonstrate that the size effect of a spindle-knot is related to the capillary adhesion of hanging-drops, thus BSF has a much higher water collection efficiency in humid environments than normal uniform fibers. The mechanism is elucidated further to open a model of high efficiency materials for water collection.