The terrestrial phase of the water cycle is conducted in watersheds arrayed like puzzle pieces across the land. Here water either Flows across impervious (or saturated) surfaces or creeps micron-by-micron through complex passages between particles of organic and mineral soil. A watershed is is also a waterhold, a vast storage basin through which water molecules creep ever downward, though slowly, slowly, seeping, oozing, always on the move, but collectively making little progress, being more held than shed.
Even during a rainstorm, the water flooding into streams is likely to be old water from previous storms, not water from the current storm Flowing over the surface of the land. New water enters the watershed from the top, pushing old water out in seeps at the bottom. Only on impervious ground or saturated soil offering no entrance to falling drops does water actually run across the surface and Flow directly into streams. More commonly, rain runs through a watershed at a creeping pace, slipping grain to grain, molecule by molecule, holding on, then letting go, holding on, letting go, billions of times a second, hour after day after month after year.
Some water takes a very long time to pass through a watershed because it is captured as groundwater and held in the lower recesses of the soil where even tree roots cannot release it. Some enters cracks in the underlying bedrock and begins a journey taking perhaps hundreds of years before it can surface miles away in another watershed altogether. Given the uneven topography of most bedrock formations, or beds of clay impervious to water--with basins here and there, low points and highpoint, steep slopes and gentle grades--some water settles into pockets cut off from the general downward Flow, and stays put (as much as water can stay put) as groundwater in a kind of underground lake or aquifer that is not open water in any sense but water actively held by--and interacting with--soil.
If the groundwater surface (water table) is close enough to the upper layer of soil, in places it forms a perennially wet area where roots are immersed in inundated (hydric) soil for weeks or months at a time, creating a wetland where plants which like wet roots can thrive, and those that don't stay away. Wetlands are a stabilizing kind of habitat, taking water in when they have storage capacity to spare, sharing it when they are full up and can't hold any more. Like erosion, wetlands are sometimes viewed suspiciously by the public--swamps, bogs, fens, marshes, vernal pools, floodplains. Not realizing the role they play in the local storage and release of life's primary resource, people sometimes drain wetlands and put them to use as farms, golf courses, subdivisions, and industrial parks. But because wetlands are places where groundwater is stored near the surface, they are missed by frogs, turtles, ducks, snails, blackbirds, alligators, snakes, muskrats, and beavers, among countless others, depending on the locale.
If a water molecule lands directly in a stream--falling as precipitation (as is has perhaps a one-in-a-hundred chance of doing), seeping into it, or running off the land--then it has a straight shot at the ocean. If, that is, it doesn't evaporate before it gets there, or become absorbed by aquatic plant or animal life, or replenish a wetland along the way. Streams and ponds are the glamorous watershed features, diverting the public eye from wetlands and deep woods. This is where the fishing is, the boating, rafting, camping, swimming. We care for aspects of nature we use and enjoy, tending to neglect those we don't. Trout and canoe trips take precedence in our minds over impassable bogs and alder thickets, though pitcher plants and stands of spruce are as much watershed products as black flies and bass.