We have a lot of water, but people don't really know exactly how it all got here. Some probably came from ice comets from outer space. Next time you drink a glass of water, you are most likely drinking water that came from an alien world! Other sources of water were from rocks that had it and released it when coming to earth. Carbon dioxide (CO2) can also react with H2S to make water, so a lot of water may have come from that too.
As far as the water we have now, precipitation and condensation are how it moves around for the most part in the from of rain and snow. The water in the ground evaporates and then condenses into clouds in the sky. When there is enough water in them, the clouds precipitate and make rain or snow.