The poem "Going for Water" by Robert Frost is narrated in the first person plural (probably by children). The narrators live in a rural environment and rely on a well for their water. Because the well has run dry, they must find an alternative source of water. They remember that there is a brook near their house but are not sure if it is actually flowing or whether it has run dry. As they head through the woods in the early evening, they are concerned not only about whether the brook still flows, but also (possibly) whether they correctly remember its location and will be able to find it in the dim light of dusk.
In the fifth stanza they hear the sound of the brook, but rather than rushing forward to look at it, they stop and listen:
Each laid on other a staying hand
To listen ere we dared to look . . .
Thus the description of the brook in the sixth stanza is based entirely on its sound rather than on sight. It describes the sound as seeming to emanate from a single place rather than from the full expanse of the brook. The phrase "tinkling fall" suggests that the part of the brook that was most audible might be a small waterfall where the brook flowed over rocks and then dropped down into a pool. This is also suggested by the metaphor of "pearls" which suggest droplets of water caught in the light rather than a smoothly flowing stream. The suggestion that sometimes droplets coalesce into a "silver blade" suggests what paddlers describe as a "tongue" or "V", a smooth but gradually narrowing strip of water at the entrance to a rapid that runs quickly and smoothly, pointing forward to a series of waves. Although this would be less dramatic in a brook than a river, it might still make a distinctive sound, especially where the end of the tongue collides with the first wave.