When India launched its first unmanned lunar probe last year, it hoped to make a splash. It appears to have achieved that in a very literal sense: the impact of the probe’s collision threw up soil samples that have offered the most compelling proof yet that there is indeed water on the moon.

Don’t pack those swimming trunks yet though: the “water” is in the form of molecules of both water and hydroxyl (which is HO rather than H20) which interact with dust and rock molecules at the very surface of the moon. In other words, what’s been discovered is closer to damp soil than a puddle.

The presence of the molecules has been confirmed from data gathered by a NASA instrument on the Chandrayaan-1 spacecraft. Carle Pieters (pictured), a professor of geological sciences at Brown University has led a team analyzing the data and has written a paper on the findings.

The researchers are still trying to figure out how the water got there and where it is going. One theory is that hydrogen-rich solar winds collided with oxygen rich soil.

The scientists believe the proportion of water in the soil could be somewhere between 770 and 1000 water molecules per million. If correct, that would mean there’s the equivalent of a 32 oz bottle of water in every ton of soil. That’s a lot of soil, but then again there’s a lot of moon.

While some enthusiasts hope that water on the moon means there’s a chance that little green men could be thriving there, NASA has more practical matters in mind. It says water would be a vital part of any permanent base on the moon and estimates that given the vast cost of lunar missions, it effectively costs $50,000 for each bottle of water taken up in a shuttle.

The findings raise new questions about lunar material brought back by the early Apollo missions. While minute amounts of water were found in some rocks, leaks in the boxes they were stored in meant it was impossible to discount the possibility that they had been contaminated on Earth.