There is water moving across the surface of the Moon right now. It's not something that would look familiar to us. The water moves as singular, isolated molecules sublimating, transitioning directly from a solid to a gas, from cold surfaces. They launch across the Moon's near vacuum in slow ballistic arcs, occasionally sinking a few centimetres into the soil before the temperature takes them permanently. It could be a resource that something might be able to intercept before it's destroyed.
That water exists as ice at the lunar poles
At some point the ice meets warmer temperatures and is slowly turned to a gas. This water vapour is in a constant slow transit. Some of it hops across the lunar surface, sailing for hundreds of kilometres, landing somewhere else until it's either destroyed by UV light or lands somewhere cold enough to stick.
Some of it sinks, diffusing down through the loosely packed grains of the lunar regolith, which experiences the daily heating and cooling cycle, until it reaches an area cool enough to freeze. Scientists call this vapour pumping.
Could a biological crust compete with physics?
Imagine a biocrust: a thin, resilient, biologically structured layer of lunar soil at the surface, similar to the crusts of cyanobacteria, lichen and fungi that carpet deserts on Earth and pull moisture out of humid air.
This biocrust could be better at catching the water vapour bouncing across the surface than the lunar regolith minerals are, and this could work in various ways. It could interrupt the hop by capturing the water on the large surface area of the crust. It could capture it with a specialised coating that is hygroscopic, basically sticky enough to hold on to the water molecule. Or it could be present at a specific depth so that it functions as a sink that actively draws moisture towards itself.
Why it's worth thinking about
New things are being discovered about the Moon all the time. A lot of what we treat as settled was actually decided decades ago. The main theories about lunar ice date back to 1961 and 1979, and right up to 2009 people were confident the Moon was completely dry. Then the LCROSS mission crashed into a crater near the pole, threw up a plume of debris, and found water in it. A certainty just dissolved.
In a different study carried out in the past few years, regarding a different process on the Moon, scientists from Manchester estimated that 270 billion tonnes of water are locked inside glass beads in the lunar soil alone.
It's worth taking a moment to think about. When we've ruled out the possibility of life somewhere for reasons such as "there's no water there," and that reason later turns out to be questionable, the response isn't to assume life is likely. It's to realise that the original thinking doesn't hold up the way it used to. At that point, the responsible step is to reopen the question.