Breen's Water is a drink that comes from a vending machine (you can see a can of water in Half - Life 2 if you press E also on a vending machine.) It makes your Citizen Character have a forgettable feeling, if you drink it. Some of the vending machines can give out other waters instead of the original like: Smooth Breen's Water and Special Breen's Water.
(ex.) Citizen: *buys a drink* Citizen: *groans* I needed this. Citizen: *drinks* Citizen: What? How did I get here? Where am I? Where did I get these clothes from? Who is that with the metal mask? *Citizen turns paranoid*