The Flood waters prevailed on the earth for 150 days in the story of Noah’s Ark.
Genesis 7:24 states that the waters prevailed for 150 days. This is a different measurement from the 40 days and 40 nights of rain described earlier. The rain duration concerns the falling rain, while the 150-day figure describes the period during which the waters remained dominant.
The narrative then moves toward the waters receding. Genesis 8:3 says the waters continually receded after 150 days, and the ark came to rest on the mountains of Ararat. The account uses several dated observations to trace the changing water level.
These separate time periods are often merged in popular summaries. The text itself, however, gives both numbers and assigns them different stages of the event. The 150-day period is therefore the best answer when the question concerns how long the waters prevailed, not how long rain fell.