Rivers of water - See the Psalms 1:3 note. As the cultivator directs the stream into the channels where it is most wanted, so Yahweh directs the thoughts of the true king, that his favors may fall, not at random, but in harmony with a divine order.
Related Commentaries of Proverbs 21:1
Proverbs 21:1
1 The king's heart is in the hand of the LORD, as the rivers of water: he turneth it whithersoever he will.