In the Genesis flood account, the waters prevailed over the earth for 150 days. Genesis 7:24 states that the waters continued to dominate the earth for this period before the recession described in the following chapter.
The 150-day figure is distinct from the forty days and forty nights of rain. Genesis mentions the rain lasting forty days and nights, then separately describes the waters prevailing for 150 days. The two numbers therefore refer to different stages or measurements in the narrative.
Genesis 8:3 says that after the 150 days, the waters began to recede. The ark later came to rest on the mountains of Ararat, and Noah continued waiting while the landscape dried.
This passage can seem confusing because the account includes several overlapping time references and dates. The safest answer to this question is the explicit duration attached to the waters prevailing: 150 days, not the duration of rainfall.