Genesis 7:11

"In the six hundredth year of Noah's life, on the seventeenth day of the second month - on that day all the springs of the great deep burst forth, and the floodgates of the heavens were opened."  Genesis 7:11

Verse 10 tells us that the floodwater came to the earth after 7 days, and now verse 11 is specifying the month and day that the waters came.  It tells us that it didn't just rain, but that springs of water came from the deep below bringing even more water to the surface.  Both Bible Ref and Bible Study Tools suggest there was a great underground ocean as well as a canopy of water encircling the globe that were let loose to flood the earth.