Some interpret Hebrews 11:7 as saying it had never rained prior to the Flood: “By faith Noah, when warned about things not yet seen, in holy fear built an ark to save his family. By his faith he condemned the world and became heir of the righteousness that comes by faith.” Rain could be the correct understanding of “things not yet seen,” or it could be referring to the Flood in general.
Genesis 2:6 says, “But streams came up from the earth and watered the whole surface of the ground.” Before the Flood (Genesis chapters 6-9), the earth was possibly surrounded by a “firmament” or canopy of water, creating a greenhouse effect on the earth’s climate. These would have been the waters that God released, causing the Flood. It seems that before the Flood the dew and ample water supply were enough to keep creation watered. The Bible does not specifically tell us whether or not it had rained before the Flood. Noah seemed to understand what rain was when God mentioned it to him (Genesis 7:4-5). Genesis 2:4-6 mentions that God did not send rain on the earth until after He created Adam and Eve. We can speculate that it had rained before the Flood, but, again, the Bible does not specifically say.