Earth's gravity really sucks when you consider space exploration, particularly human space exploration. One of the problems with going to Mars is that the humans must carry enough water and food for the trip. Food can be dehydrated, which reduces the weight considerably so scientists and engineers are concentrating on how to get all that water to Mars and back. One proposal is to go to the moon first, set up a base there and collect ice for journeys further afield. Since the moon has only one sixth Earth's gravity, this reduces the problem considerably. Of course, you want to be pretty sure that the moon had water before launching.
One of the leading candidates for containing ice was the Shackleton crater, located at the Moon's south pole. Ice reflects radar in an unusual way, being quite shiny it reflects more radar signal than dense rock. It also preserves the radar polarization (the orientation of the electric field) more. Hence by measuring both the amplitude and polarization of the reflected signal, one can infer the presence of ice, provided you have some other evidence to eliminate other, similar scatterers. Radar images formed the majority of the evidence for water in the Shackleton crater because the signal was ice-like and some parts of the crater are dark for extended periods of time and, correspondingly, the temperature was low—must be water, right?
Well, wrong as it turns out. Researchers have made high resolution radar images to separate out the reflection signal from various sections of the crater. This allowed them to determine that the "ice" signal did not correlate with dark areas of the crater, which implies that another scatterer, most likely rocky debris, is a more likely explanation.
This does not totally eliminate the possibility of water on the moon. Nasa's Lunar explorer picked up evidence of ice from the Shackleton crater using neutron spectroscopy. However, these new measurements eliminate the possibility of the ice concentration being above 2 percent. That means those ice miners will be grubbing through tonnes of rock for a few liters of water, which is not an attractive prospect.