How does water erode rock?
Water does not melt rocks; rocks melt at temperatures that would long ago have boiled water. However, water can help erode rocks because when water freezes into ice, it expands. As a result, when water gets into cracks in the rock surface and subsequently freezes, the expansion pressure breaks the rocks into smaller pieces.
== == Rain water contains carbonic acid which slowly dissolves rocks, especially the carbonate variety, such as limestone. Moving water carries small rock particles to larger and larger bodies of water, until they may end up in the ocean as silt, clay, and sand. Water freezing in the cracks of rocks acts like a jack, prying the rocks into smaller and smaller pieces. And water acts as a chemical catalyst, dissolving elements from rock and carrying them away as described above. Frozen water in the form of glaciers can scour a landscape of earth, rocks, and everything else in its path.