5:15-18 The wife is pictured as the source of water in these images of “cistern,” “well,” “springs,” “streams,” and “fountain,” which is clear both in the repeated phrase from your own cistern/well (v.15) and the conjunction of “your fountain” and the wife of your youth (v. 18).
– ESV Study Bible, 1143 (emphasis mine)
“I … don’t know how one can miss all the words in Proverbs 5 that describe wives as ‘fountains,’ ‘springs,’ ‘cisterns’ and ‘wells’ from which a man drinks ‘water,’ ‘running water’ and ‘streams of water.'”
The force of v. 16 is thus to call the hearer to imagine how he would feel if his wife were to commit adultery (Should your springs be scattered abroad, streams of water in the streets?) and to follow the principle of doing unto others what you would have done to you (see Matt. 7:12; Luke 6:31), i.e., be faithful to her as he wishes her to be faithful to him.
5:18-19 Proverbs calls unabashedly for seeking fulfillment in the sexual intimacy of marriage (Let her breasts [drench] you at all times … be intoxicated) as the relational context where these desires are rightly fostered for the enjoyment (rejoice in the wife of your youth) and good (Let your fountain be blessed) of both husband and wife. (Regarding “be intoxicated,” see ESV footnote: Hb. “be led astray” — i.e., in the sense of being “swept away” with delight in one’s wife.)
– ESV Study Bible, 1143