Psalm 104:9 (ESV)

9 You set a boundary that they may not pass, so that they might not again cover the earth.

In this verse it is made very clear that God determines the boundaries for the turbulent bodies of water. God also explicitly promised this to Noah and his sons and to all living creatures: Never again shall all flesh be cut off by the waters of the flood, and never again shall there be a flood to destroy the earth (Genesis 9:11). The rainbow in the clouds serves as a sign of this covenant. This colourful rainbow in the clouds is a sign for God and for us of this everlasting covenant (Genesis 9:16). Based on this promise of God, the earth is a safe place for man and animals.