Speaking of fountains, that water imagery in the last stanza seems to come out of nowhere. Still, Glück has prepared us for it by including a single contrasting reference to dryness early in the poem. Rich with symbolism, the image of the great fountain is connected to life, while absence of water is associated with death.
Line 7: Here's that "dry surface." Irises prefer full sun and moist soil. Yet this setting supplies only weak sunlight and precious little water. A wild iris could die in conditions like that. Quick, grab the watering can!
Lines 18-22: We find no further mention of water (or lack thereof) until the image of the fountain in the final stanza, but we need to back up a few lines to understand what the fountain is all about. The colon at the end of line 20 equates the fountain with "voice," the ability to "speak again."
Line 23: Why is the fountain composed of "seawater"? There's no right answer to that question, so feel free to free-associate. The ocean is often viewed as the universal source of life, and our own bodies contain both water and salts. The poem's few details of setting (pine tree, low shrubs) seem unrelated to the ocean, but Iris, the Greek goddess of the rainbow, links the sea and sky. She also connects humans with the gods. So the image of the fountain suggests spiritual, as well as emotional, power.