If the Lone Wanderer has sabotaged Project Purity with President Eden's modified F.E.V., there will be a couple new dialogue options available when speaking with Brother Gerard. Gerard can be told that one can relate to "Tainting water under the guise of helping humanity," or express panic at the realization that they have just drunk F.E.V.-infected Aqua Pura.
↑Fallout 3 Official Game Guide Game of the Year Edition p.64: "Brother Gerard First officer of the Apostles of the Eternal Glow, this evangelical off-shoot of the Church of the Atom has plans to sweep the Wasteland by beckoning their followers to bathe in "light." Gerard is direct and friendly to a point, but keen to further the Church's causes no matter what the cost. If you run into Brother Gerard after a nearby nuclear explosion, he greets his new and terminally singed appearance as the ultimate sign on his path to radioactive righteousness." (Fallout 3 Official Game Guide Game of the Year Edition Wasteland Census)