The moon has practically no atmosphere. Any light elements or compounds deposited on the lunar surface by possible out-gassing or comet fragments and meteorites are subject to direct exposure to the vacuum of space. Over the course of a lunar day, about 29 Earth days, all exposed surfaces of the moon are bathed in sunlight with daylight temperatures reaching up to 250° Fahrenheit (121° C.) Any ice exposed to sunlight for any length of time would turn into water vapor, break apart and be lost to space.
Water could only exist in areas of permanent shadow and those areas exist at the lunar poles. Some of these crater floors have not seen sunlight for possibly billions of years. Temperatures within these crates do not go above –280° F (-173° C) so they act as ‘cold traps’ where even light elements or compounds don’t have enough energy to evaporate.