Here's why:

* Cold Traps: These craters never receive direct sunlight, making them extremely cold. This cold environment acts as a "trap" for water molecules, preventing them from evaporating back into space.

* Ice Deposits: Spectral analysis of these craters has confirmed the presence of water ice mixed with other materials like dust and regolith.

* Hydrated Minerals: Additionally, water is also found in hydrated minerals scattered across the lunar surface.

While some water vapor is present in the lunar atmosphere, it's in very small amounts and not considered a major reservoir.