Subsurface ice in cold hyperarid conditions retreats by sublimation and diffusion through the overlying soil layer. Here, it is shown that percolating meltwater, if present, can counterbalance sublimation loss effectively and thus increase the persistence time of subsurface ice. Time averaging of transport equations is used to evaluate the significance of percolation in an otherwise complex dynamical system. The reduction in sublimation loss is approximately given by the amount of meltwater multiplied by the percolation depth and divided by the depth to the ice table. It is plausible that percolation is even more effective during a warmer, wetter climate. Copyright © 2009 John Wiley & Sons, Ltd.