Some interpret Hebrews 11:7 as saying it had never rained prior to the Flood: “By faith Noah, being warned of God of things not seen as yet, moved with fear, prepared an ark to the saving of his house; by the which he condemned the world, and became heir of the righteousness which is by faith.” Rain could be the correct understanding of “things not yet seen,” or it could be referring to the Flood in general. “But there went up a mist from the earth, and watered the whole face of the ground.” Genesis 2:6
Before the Flood (Genesis chapters 6-9), the earth was 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. 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).
“These are the generations of the heavens and of the earth when they were created, in the day that the Lord God made the earth and the heavens, And every plant of the field before it was in the earth, and every herb of the field before it grew: for the Lord God had not caused it to rain upon the earth, and there was not a man to till the ground. But there went up a mist from the earth, and watered the whole face of the ground.” Genesis 2:4-6 In this account 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.