“This purifier would provide clean water to Underpass, if it were functional. Whoever assembled it had no idea what they were doing - many parts are connected incorrectly or hooked up backwards. Someone with the proper knowledge could easily get the purifier operational.”
Underpass was going to be a settlement north of New Vegas, but was cut from the final retail release of the game.
Carlyle St. Clair's house would have existed within the town, and according to the cell name, there would have been a purifier close by.