In Part 2 of Fahrenheit 451, water is used to signify three things: life, knowledge, or death. First, Captain Beatty quotes Pope about the Pierian spring in order to make a point to Montag:
"A little learning is a dangerous thing. Drink deep, or taste not the Pierian spring; There shallow draughts intoxicate the brain, and drinking largely sobers us again" (106).
Since the Pierian spring is believed to be a fountain of knowledge, it is easy to connect water with knowledge in this allusion. Beatty says that Montag became a "drunkard" for a little while as he was reading books and adding to his well of knowledge. In response to Beatty's arguments, Faber counters by telling Montag, "He's muddying the water!" (107). It is interesting that Faber uses water imagery as he warns Montag not to allow himself to become confused by everything that Captain Beatty is saying. Faber uses "muddying" to suggest that Beatty is making things dirty, or confused. Basically, Faber wants Montag to know that Beatty is taking words and quotes out of context to fit his argument and to be aware of it. This also suggests that knowledge is only good if it is clean, clear and honest. If a person learns incorrect facts, for example, then the knowledge is useless or muddy.
Next, when Faber is teaching Montag about why books are hated and feared in their society, he uses an analogy of how flowers grow. Flowers are a part of the circle of life and they need water, sun, and dirt to live. Society also has a cycle that should involve knowledge, love and fun (among other things); but their society only values fun. Faber says the following:
"We are living in a time when flowers are trying to live on flowers, instead of growing on good rain and black loam. . . Yet somehow we think we can grow, feeding on flowers and fireworks, without completing the cycle back to reality" (83).
In the above quote, rain (water) is an essential part of a flower's growth and life. Faber is suggesting that their society is missing knowledge as an essential part of the cycle of human life; and as shown above, water also represents knowledge. Faber is saying that their society is missing this one key ingredient that would help them recognize reality. As it is, everyone in their city lives on pleasure-seeking fantasies rather than the search for knowledge and reality.
Finally, water can represent death, and, playing with the analogy that water equals knowledge, a person without knowledge isn't really living. However, Captain Beatty has a lot of knowledge and can verbally counter-attack anything Montag might say in favor of learning and reading. So, Montag asks Faber to help him when he faces Beatty again. Montag references water by asking Faber the following:
"Can you help me in any way tonight, with the Fire Captain? I need an umbrella to keep off the rain. I'm so damned afraid I'll drown if he gets me again" (89).
This quote shows that Captain Beatty can fire off a rainstorm of information at Montag before he can defend his position. The rain (water) mentioned here represents Beatty's knowledgeable comments pouring down on Montag to the point that he might drown and lose the verbal battle. In this case, water (knowledge) is used to dampen one's spirits rather than to uplift and edify.