The Waters of Life

 is a Fallout 3 quest. It is also an Xbox 360 achievement.

The quest is about reactivating the abandoned Project Purity, a water filtering facility set up 19 years before at the Jefferson Memorial.

James quotes the following Bible passage in the tutorial: "I am Alpha and Omega, the beginning and the end. I will give unto him that is athirst of the fountain of the water of life freely."

During the Quest, you must first clear out the area for the scientists (Dr. Li and her fellow scientists, and your dad).

After clearing the basement, the museum/gift shop and the rotunda, your father sends you on some routine maintenance missions, to bring the project back online. After draining some of the flooding, replacing the door control fuses and reactivating the mainframe, your father sends you off to remove some blockages in a pipe.

During this time the Enclave attacks. You must fight your way through a few Enclave soldiers in power armor to reach your father. When you arrive at the control room, Dr. Li is locked out of the main area, while a scientist, your father, an Enclave colonel and 2 Enclave soldiers are locked in. You are forced to watch the officer execute the scientist to get your dad to give up control of the project and help Enclave scientists get it online. Your father admits defeat and heads over to the controls, seeming like he will help them. Instead he uses the controls to flood the area with radiation, killing the Enclave soldiers and officer. You see your father one last time at the glass, before he says "run...." and collapses dead. You can get into the locked area before the emergency door closes, but you will be stuck inside and the conversation will stop if you interact with your father or the colonel.

You must then escort Dr. Li and the remaining scientists (they do not have to survive) through the sewers via an emergency secret exit. Inside you will face feral ghouls and plenty of Enclave soldiers. In the entrance of the second section of the tunnels (Taft Tunnel), Li will stop and demand medical aid for Garza, who has a heart condition. You can give her 5 stimpacks to help him, or try to convince her to leave him behind. There is also the option to hand over 3 Buffouts which Dr. Li will use to drug Garza to keep him moving.

At the end of the tunnel, you arrive at the Brotherhood of Steel Citadel, and complete the quest. This quest also unlocks the ability to train in power armor, and you have 24 hours (not sure if this is true, I found the distress signal long after I first visited the Citadel) to visit Vault 101 to complete a quest inside there (picking up a bobblehead that can be missed at the start of the game).