> 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. 12 And rain fell on the earth forty days and forty nights.
http://www.biblegateway.com/passage/?search=Genesis%207&vers...
They believed that they were on a flat earth under a dome that separated the atmosphere from huge amounts of water above (hence the blue color of the sky) and below (hence the oceans). They believed that the dome leaked sometimes, causing rain. They believed that the flat earth leaked too, causing rivers.
More information here: http://en.wikipedia.org/wiki/Biblical_cosmology