""To lay something bare" basically means to reveal or expose something. From the context you gave, it could be used like "we are being exposed". In the third sentence, it sounds like the word should be 'line' the walls not 'lime', are you sure it was definitely 'lime'? I hope this helps a little!

Our waters are receding: The level of the waters are becoming lower. Наши воды спадают. Faint white rings of past levels lime the walls: When water reaches a certain level, remains there a while, and then recedes, it leaves a mark at the level it remained at for a while. This mark is often called a "ring", especially if the mark is somewhat circular." It seems that the waters contained a chemical called "lime". Lime is известь, which is white. Each time the waters reached a certain level, they left a white mark (ring) on the walls. In your sentence, "lime" is being used as a verb. Because floodwaters reached various levels in the past, the white marks made in the past at different levels were "faint" (тусклый, слабый).

It sounds like the context is a flood that has covered something up, perhaps a building as "walls" are mentioned. But as the flood waters fall, the structure is exposed ("laid bare"). You can see the white rings on the walls showing how high the water rose. But this isn't the first time this has happened, and you can see deposits from previous floods, rather like successive coats of limewash paint that has been applied to masonry with patchy effect.

"Laid bare" is a literary way of saying "devastated". "Lime" in this context is a verb meaning "to mark or cover".