Just about everything!
Water is the most powerful erosional agent on the planet! It's responsible for more physical breakdown of matter than any other agent, both chemical or physical. Water, when in its liquid form, is remarkably more dense than its frozen form. So when liquid water gets into the porous spaces and cracks in rocks, it will expand once it freezes, physically pushing the rocks apart. This is call frost wedging.
Water running against rock, like you'd see at a waterfall or a river, breaks apart rocks and other matter, and moves them away from the source (water is also an excellent transport agent). This occurs very slowly, by our standards, but fairly quickly on a geological time scale.