The words of a man's mouth are as deep waters. "Man" (ish) here means the ideal man in all his wisdom and integrity, just as in Proverbs 18:22 the ideal wife is intended under the general term "wife."
Such a man's words are as deep waters which cannot be fathomed or exhausted. The metaphor is common (see Proverbs 20:5; Ecclesiastes 7:24; Ec 21:13). For "mouth," the Septuagint reads "heart:" "Deep water is a word in a man's heart."
The second hemistich explains the first: The well spring of wisdom as a flowing (gushing) brook. A man's words are now called a well spring of wisdom, gushing forth from its source, the wise and understanding heart, pure, fresh, and inexhaustible.
Septuagint, "And it leapeth forth ( 慣?館慣?管灌??琯菅) a river and a fountain of life." Or we may, with Delitzsch, take the whole as one idea, and consider that a man's words are deep waters, a bubbling brook, and a fountain of wisdom.