The Moon is completely dry.

The Apollo missions returned rocks from a landscape that looked completely dry. Early laboratory studies found no convincing reservoir of native lunar water, and tiny traces could easily be blamed on contamination after the samples reached Earth.

For decades, the Moon was therefore described as essentially or completely dry.

Better instruments changed that conclusion.

When Apollo samples were reanalyzed with more sensitive methods, researchers found small amounts of water preserved inside volcanic glass beads and minerals. Because that water was trapped within lunar material, it showed that some water had existed inside the Moon rather than arriving only as contamination on Earth.

Spacecraft added evidence from the surface. Instruments detected hydrogen near the lunar poles and spectral signatures of water or hydroxyl in other regions. Hydroxyl is a chemical group containing one oxygen and one hydrogen atom; it is related to water but is not the same molecule.

The largest concentrations of lunar water occur in permanently shadowed polar craters. Sunlight never reaches some of these cold areas, allowing water ice to survive for very long periods.

The correction should not be exaggerated. The Moon has no oceans, lakes, or widespread liquid water and is still extraordinarily dry compared with Earth. Most lunar water occurs in tiny concentrations, chemically bound in materials, or frozen in cold traps.