The title gives a clue: "aqueous humor" is the clear fluid inside the eye, so the poem keeps blurring the line between water we drink or see and the water that helps us see. It starts with something small, water from a glass, then calls it "strong water," as if it carried real force. Then the view widens. The speaker seems to take in a boat or a pretty little bridge, which could be a real scene or a reflection, and the poem lets that uncertainty stand.
The water becomes a "body of water singing / some other knowledge," a nice phrase for a kind of understanding that comes through feeling rather than explanation. The last lines, "saving my eyes / all the night," suggest the speaker is soothed, perhaps comforted through a sleepless or dark stretch. The mood is quiet, tender and a little mysterious, with a sense of gratitude toward something simple and clear.