Groundwater provides drinking water for 50% of people in the US. Lakes and ponds are bodies of still surface water, with ponds generally being smaller than lakes. Rivers and streams flow with water from runoff and precipitation. Wells collect groundwater from underground, while springs release groundwater and geysers release hot water. The water cycle describes the continuous movement of water above and below the Earth's surface through evaporation, condensation, and precipitation. Tides are caused by the gravitational pull of the moon and sun distorting ocean waters. Humans can impact water through displacing it when entering, unintentionally removing water droplets, and pollution from littering and oil spills.