Sukah 48b, according to Rashi: This is the source to blow trumpets when bringing the water for Nisuch ha'Mayim.

Rashi citing Targum Yonasan: You will receive new learning. Radak - Chachmah is metaphorically called water. The teachers are like a spring, and the Talmidim draw. It will be a new learning, and they will learn to know Hashem, what no one learned until that day - "ka'Mayim la'Yam Mechasim" (11:9).

Radak: This is a metaphor - just like one who draws water from a spring that never ceases, he always finds water to draw, so the Brachah and salvation will not cease. They will rejoice all their days.

Malbim: Not only will they not fear lest the salvation pass from them. They will also attain new salvations from time to time. It is as if springs of salvation are opened. Doleh is drawing from deep wells, which is exertion; Sho'ev is drawing without toil. The Nimshal is attaining new salvations without toil.

Rashi: He will widen their hearts via the salvation, and secrets of Torah will be revealed to them that were forgotten in Bavel via afflictions.