"Water and Rock" is an extract from section 5. It names “What the thunder said”.
According to the poet, these lines are the best of the whole poem.
The title is a reference to the Indian legend of the thunder: after the thunder it rains. The legend belongs to Upanishad.
Eliot said that in the first part of the fifth section he employed three themes: journey to Emmaus; approach to the Chapel Perilious; eastern Europe decay
To tell the truth the legend of the thunder may also be a reference to the vegetation rites.
The scene refers to some people walking upwards to reach the Chapel Perilious. The weather is terribly arid and sterile, very hot and the people have got sweaty faces.
The atmosphere is still a difficult one.
The scene is totally built up with an insistent use of the objective correlative, namely water and rock. The people are very hot and sweaty.
There is an atmosphere of agony, where you can hear shouting and crying. They seem to be imprisoned and trapped. You can hear the echo of thunderous spring in the distant mountains.
There is the same atmosphere of dying. The landscape is a rocky one, where there is not even the memory of water.
Water is a metonymy for baptism, a ritual by means of which men are purified from their sins.
There is the rendering of the fatigue because the road is going above and it’s not straight forward. But at the top they find only rock and no water.