“person who blesses others.” The Hebrew reads, “the soul of blessing,” where “soul” refers to an individual and “a person of blessing” is a person who blesses others.
“prosperous.” The literal Hebrew is “fat.” Proverbs 11:25 is one of the many “ideal” promises in the Word of God which would be fulfilled here on earth today if we lived in a godly world with godly people. But because there are evil people and the Devil is the god of this age (2 Cor. 4:4; 1 John 5:19), people who help others do not always prosper in this life. This promise will only be fully fulfilled in the future. [For more on promises like this, see commentary on Prov. 19:5].
“will be watered.” The Hebrew in the Hophal aspect more literally reads, “will be taught.” This sheds light on what the verse is speaking of when it talks about watering others; there is a primary influence in instructing them. Then, the instructor himself learns more as well. But the verbs refer to more than just teaching and being taught because they are being used metaphorically. There are many ways to water others, but teaching is a primary one, especially in the larger context of Proverbs, with all its emphasis on gaining wisdom and understanding.