We have investigated the variability of the appearance of the residual north polar cap and its connection to Mars' water cycle. Previous studies interpreted differences in ice coverage between Mariner 9 and Viking Orbiter observations of Mars' residual north polar cap as evidence of interannual deposition on the cap. Our more comprehensive analysis shows that the appearance of the residual polar cap does not show large-scale variance on an interannual basis. Rather we find evidence that regions that were dark in the summer season grow bright later in the summer. We believe deposition of water ice can account for the brightening, and discuss temperature, albedo and water vapor data to support this argument. Additionally, we have used Mie theory and a Delta-Eddington approximation for radiative transfer to quantify the accumulation of water ice and dust sufficient to explain the brightening.