The selenographic locations and measurements of such morphological characteristics as length, width, meander wavelength, and minimum average depth have been obtained for about 130 lunar sinuous rilles. We conclude that the morphology of the sinuous rilles requires that they be features of surface water erosion, which could occur in the present lunar environment, since a layer of ice can pressurize the water and maintain it in a liquid phase. Water is assumed to be trapped beneath a permafrost layer, which is shown to be stable on a geologic time scale. The concentration of the rilles around the circular mare basins and in craters with mare-type floors implies a concentration of water and other volatiles along the margins of such circular basins and craters and associates the outgassing of the lunar interior with major impacts. The rille meander pattern is characterized by a median wavelength to width ratio >4, a value not inconsistent with ratios found for terrestrial alluvial rivers. The generally smaller ratio of meander wavelength to width for lunar sinuous rilles than for terrestrial rivers may indicate that the lunar rivers responsible for eroding the rilles transported a larger percentage of suspended-load material than is carried by terrestrial rivers. We estimate that the amount of water ultimately available on the lunar surface is two orders of magnitude greater than that required to erode all the sinuous rilles. This estimate of the available water is in agreement with the measured water content of the Apollo 11 lunar samples.