The time it takes for a water molecule to complete a full circuit of Earth's oceans is known as the "global oceanic circulation time." The exact duration can vary depending on the specific pathway taken by the water and the circulation patterns of the oceans. However, on average, it is estimated to take about 1,000 years for a water molecule to complete a full cycle through the global oceanic circulation.
This estimate takes into account the various processes involved in oceanic circulation, including surface currents, deep-ocean currents, upwelling, and mixing. Surface currents, driven by wind patterns, are relatively faster and can complete a circuit in a matter of years or decades. Deep-ocean currents, which are driven by differences in water density and temperature, can take much longer, potentially hundreds or even thousands of years, to complete a full circuit.