The Waters of Life

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

The quest centers around the reactivation of the abandoned Project Purity, a water filtering facility set up 19 years before at the Jefferson Memorial in an attempt to bring large quantities of clean water to the Capital Wastes. James and Dr. Li were unsuccessful originally, but after meeting with Stanislaus Braun in Vault 112 (Tranquility Lane), he believes he has the solution.

Go To the Rivet City Science Lab / Join the scientists at Project Purity
Your father is going back to Rivet City; you can choose to follow him or let him go on his own and meet him later. Either way, he'll run there while you're close to him and walk while you aren't, but will get there eventually.

When you arrive at Rivet City Science Lab, Your father convinces Dr. Li to reactivate Project Purity, after talking to him he asks you to meet him and the scientists there.

Clear Project Purity of any remaining Mutant Threat
Your Dad instructs you to first clear out the area, most of the Super Mutants in the Gift shop should have been killed by you in the Scientific Pursuits Quest, however you must also go to the basement and clear out the Mutants there. You objectives will update when all have been killed.

Return to your Dad, and escort your him and the scientists into the control room.

If you've already cleared out the Jefferson Memorial completely, your father and the team will go straight to the Rotunda, bypassing the preliminary pep-talk.

Routine maintenance
Once Your father arrives at the control room, he asks you to carry out some routine maintenance missions to bring the project back online.
 * Turn on Flood Control Pump Power - Simply activate the control in the basement.
 * Get the Fuses from Dad / Replace Damaged Fuses - Return to your father to get new fuses, and then return to the basement activate the fuse box to replace the fuses
 * Boot up the mainframe / Speak with Dad over intercom - Activate the Mainframe, then talk though one of the intercoms where your father sends you off to remove some blockages in a pipe.

Drain the Intake Pipes
Once inside the pipe, you arrive at a section where a locked door prevents you from going further, on the right is the valve to active, once activated, you witness the Enclave arriving.

Return to the Control room
Fight your way back to the control room facing the 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.

Escort Doctor Li to the evacuation point & Taft Tunnel
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 convince Dr. Li to use 3 units of Buffout, which she will use to drug Garza to keep him moving.

Note: If you don't wish to leave Garza or you don't have Buffout or high speechcraft, it is possible to continue along the corridors by yourself and procure 5 Stimpacks. They are in 2 locations, the first is and abandoned operating theatre which is to the left when the corridor forks off not long after Garza has to stop. The second location is at the very end of the corridors, directly behind the Brotherhood of Steel barricade, in a first aid container.

At the end of the tunnel, you arrive at the Brotherhood of Steel Citadel, completing the quest and leading immediately into Picking up the Trail.